HER2-Low Breast Cancer: Pathological and Clinical Landscape

Modi S., Park H., Murthy R.K., Iwata H., Tamura K., Tsurutani J., Moreno-Aspitia A., Doi T., Sagara Y., Redfern C., Krop I.E., Lee C., Fujisaki Y., Sugihara M., Zhang L., et. al.

PURPOSE Trastuzumab deruxtecan (T-DXd, formerly DS-8201a) is a novel human epidermal growth factor receptor 2 (HER2)-targeted antibody drug conjugate (ADC) with a topoisomerase I inhibitor payload. A dose escalation and expansion phase I study evaluated the safety and activity of T-DXd in patients with advanced HER2-expressing/mutated solid tumors. Here, results for T-DXd at the recommended doses for expansion (RDE) in patients with HER2-low (immunohistochemistry [IHC] 1+ or IHC 2+/in situ hybridization−) breast cancer (ClinicalTrials.gov identifier: NCT02564900 ) are reported. PATIENTS AND METHODS Eligible patients had advanced/metastatic HER2-low–expressing breast cancer refractory to standard therapies. The RDE of 5.4 or 6.4 mg/kg T-DXd were administered intravenously once every 3 weeks until withdrawal of consent, unacceptable toxicity, or progressive disease. Antitumor activity and safety were assessed. RESULTS Between August 2016 and August 2018, 54 patients were enrolled and received ≥ 1 dose of T-DXd at the RDE. Patients were extensively pretreated (median, 7.5 prior therapies). The confirmed objective response rate by independent central review was 20/54 (37.0%; 95% CI, 24.3% to 51.3%) with median duration of response of 10.4 months (95% CI, 8.8 month to not evaluable). Most patients (53/54; 98.1%) experienced ≥ 1 treatment-emergent adverse event (TEAE; grade ≥ 3; 34/54; 63.0%). Common (≥ 5%) grade ≥ 3 TEAEs included decreases in neutrophil, platelet, and WBC counts; anemia; hypokalemia; AST increase; decreased appetite; and diarrhea. Three patients treated at 6.4 mg/kg suffered fatal events associated with T-DXd–induced interstitial lung disease (ILD)/pneumonitis as determined by an independent adjudication committee. CONCLUSION The novel HER2-targeted ADC, T-DXd, demonstrated promising preliminary antitumor activity in patients with HER2-low breast cancer. Most toxicities were GI or hematologic in nature. ILD is an important identified risk and should be monitored closely and proactively managed.

Suurs F.V., Lub-de Hooge M.N., de Vries E.G., de Groot D.J.

Bispecific antibodies (bsAbs) are antibodies that bind two distinct epitopes to cancer.. For use in oncology, one bsAb has been approved and 57 bsAbs are in clinical trials, none of which has reached phase 3. These bsAbs show great variability in design and mechanism of action. The various designs are often linked to the mechanisms of actions. The majority of bsAbs engage immune cells to destroy tumor cells. However, some bsAbs are also used to deliver payloads to tumors or to block tumor signaling pathways. This review provides insight into the choice of construct for bsAbs, summarizes the clinical development of bsAbs in oncology and identifies subsequent challenges.

Hurvitz S.A., Martin M., Jung K.H., Huang C., Harbeck N., Valero V., Stroyakovskiy D., Wildiers H., Campone M., Boileau J., Fasching P.A., Afenjar K., Spera G., Lopez-Valverde V., Song C., et. al.

PURPOSE The KRISTINE study compared neoadjuvant trastuzumab emtansine plus pertuzumab (T-DM1+P) with docetaxel, carboplatin, trastuzumab plus P (TCH+P) for the treatment human epidermal growth factor receptor 2–positive stage II to III breast cancer. T-DM1+P led to a lower pathologic complete response rate (44.4% v 55.7%; P = .016), but fewer grade 3 or greater and serious adverse events (AEs). Here, we present 3-year outcomes from KRISTINE. METHODS Patients were randomly assigned to neoadjuvant T-DM1+P or TCH+P every 3 weeks for six cycles. Patients who received T-DM1+P continued adjuvant T-DM1+P, and patients who received TCH+P received adjuvant trastuzumab plus pertuzumab. Secondary end points included event-free survival (EFS), overall survival, patient-reported outcomes (measured from random assignment), and invasive disease-free survival (IDFS; measured from surgery). RESULTS Of patients, 444 were randomly assigned (T-DM1+P, n = 223; TCH+P, n = 221). Median follow-up was 37 months. Risk of an EFS event was higher with TDM-1+P (hazard ratio [HR], 2.61 [95% CI, 1.36 to 4.98]) with more locoregional progression events before surgery (15 [6.7%] v 0). Risk of an IDFS event after surgery was similar between arms (HR, 1.11 [95% CI, 0.52 to 2.40]). Pathologic complete response was associated with a reduced risk of an IDFS event (HR, 0.24 [95% CI, 0.09 to 0.60]) regardless of treatment arm. Overall, grade 3 or greater AEs (31.8% v 67.7%) were less common with T-DM1+P. During adjuvant treatment, grade 3 or greater AEs (24.5% v 9.9%) and AEs leading to treatment discontinuation (18.4% v 3.8%) were more common with T-DM1+P. Patient-reported outcomes favored T-DM1+P during neoadjuvant treatment and were similar to trastuzumab plus pertuzumab during adjuvant treatment. CONCLUSION Compared with TCH+P, T-DM1+P resulted in a higher risk of an EFS event owing to locoregional progression events before surgery, a similar risk of an IDFS event, fewer grade 3 or greater AEs during neoadjuvant treatment, and more AEs leading to treatment discontinuation during adjuvant treatment.

Banerji U., van Herpen C.M., Saura C., Thistlethwaite F., Lord S., Moreno V., Macpherson I.R., Boni V., Rolfo C., de Vries E.G., Rottey S., Geenen J., Eskens F., Gil-Martin M., Mommers E.C., et. al.

Trastuzumab duocarmazine is a novel HER2-targeting antibody-drug conjugate comprised of trastuzumab covalently bound to a linker drug containing duocarmycin. Preclinical studies showed promising antitumour activity in various models. In this first-in-human study, we assessed the safety and activity of trastuzumab duocarmazine in patients with advanced solid tumours.We did a phase 1 dose-escalation and dose-expansion study. The dose-escalation cohort comprised patients aged 18 years or older enrolled from three academic hospitals in Belgium, the Netherlands, and the UK with locally advanced or metastatic solid tumours with variable HER2 status who were refractory to standard cancer treatment. A separate cohort of patients were enrolled to the dose-expansion phase from 15 hospitals in Belgium, the Netherlands, Spain, and the UK. Dose-expansion cohorts included patients aged 18 years or older with breast, gastric, urothelial, or endometrial cancer with at least HER2 immunohistochemistry 1+ expression and measurable disease according to Response Evaluation Criteria in Solid Tumors (RECIST). Trastuzumab duocarmazine was administered intravenously on day 1 of each 3-week cycle. In the dose-escalation phase, trastuzumab duocarmazine was given at doses of 0·3 mg/kg to 2·4 mg/kg (3 + 3 design) until disease progression or unacceptable toxicity. The primary endpoint of the dose-escalation phase was to assess safety and ascertain the recommended phase 2 dose, which would be the dose used in the dose-expansion phase. The primary endpoint of the dose-expansion phase was the proportion of patients achieving an objective response (complete response or partial response), as assessed by the investigator using RECIST version 1.1. This ongoing study is registered with ClinicalTrials.gov, number NCT02277717, and is fully recruited.Between Oct 30, 2014, and April 2, 2018, 39 patients were enrolled and treated in the dose-escalation phase and 146 patients were enrolled and treated in the dose-expansion phase. One dose-limiting toxic effect (death from pneumonitis) occurred at the highest administered dose (2·4 mg/kg) in the dose-escalation phase. One further death occurred in the dose-escalation phase (1·5 mg/kg cohort) due to disease progression, which was attributed to general physical health decline. Grade 3-4 treatment-related adverse events reported more than once in the dose-escalation phase were keratitis (n=3) and fatigue (n=2). Based on all available data, the recommended phase 2 dose was set at 1·2 mg/kg. In the dose-expansion phase, treatment-related serious adverse events were reported in 16 (11%) of 146 patients, most commonly infusion-related reactions (two [1%]) and dyspnoea (two [1%]). The most common treatment-related adverse events (grades 1-4) were fatigue (48 [33%] of 146 patients), conjunctivitis (45 [31%]), and dry eye (45 [31%]). Most patients (104 [71%] of 146) had at least one ocular adverse event, with grade 3 events reported in ten (7%) of 146 patients. No patients died from treatment-related adverse events and four patients died due to disease progression, which were attributed to hepatic failure (n=1), upper gastrointestinal haemorrhage (n=1), neurological decompensation (n=1), and renal failure (n=1). In the breast cancer dose-expansion cohorts, 16 (33%, 95% CI 20·4-48·4) of 48 assessable patients with HER2-positive breast cancer achieved an objective response (all partial responses) according to RECIST. Nine (28%, 95% CI 13·8-46·8) of 32 patients with HER2-low, hormone receptor-positive breast cancer and six (40%, 16·3-67·6) of 15 patients with HER2-low, hormone receptor-negative breast cancer achieved an objective response (all partial responses). Partial responses were also observed in one (6%, 95% CI 0·2-30·2) of 16 patients with gastric cancer, four (25%, 7·3-52·4) of 16 patients with urothelial cancer, and five (39%, 13·9-68·4) of 13 patients with endometrial cancer.Trastuzumab duocarmazine shows notable clinical activity in heavily pretreated patients with HER2-expressing metastatic cancer, including HER2-positive trastuzumab emtansine-resistant and HER2-low breast cancer, with a manageable safety profile. Further investigation of trastuzumab duocarmazine for HER2-positive breast cancer is ongoing and trials for HER2-low breast cancer and other HER2-expressing cancers are in preparation.Synthon Biopharmaceuticals.

Cardoso F., Kyriakides S., Ohno S., Penault-Llorca F., Poortmans P., Rubio I.T., Zackrisson S., Senkus E.

Mittendorf E.A., Lu B., Melisko M., Price Hiller J., Bondarenko I., Brunt A.M., Sergii G., Petrakova K., Peoples G.E.

Abstract Purpose: In phase I/II studies, nelipepimut-S (NP-S) plus GM-CSF vaccine was well tolerated and effectively raised HER2-specific immunity in patients with breast cancer. Results from a prespecified interim analysis of a phase III trial assessing NP-S + GM-CSF are reported. Patients and Methods: This multicenter, randomized, double-blind phase III study enrolled females ≥18 years with T1–T3, HER2 low–expressing (IHC 1+/2+), node-positive breast cancer in the adjuvant setting. Patients received 1,000 μg NP-S + 250 μg GM-CSF or placebo + GM-CSF monthly for 6 months, then every 6 months through 36 months. The primary objective was disease-free survival (DFS). Protocol-specified imaging occurred annually. New abnormalities were categorized as recurrence events; biopsy confirmation was not mandated. The interim analysis was conducted as specified in the protocol after 73 DFS events. Results: A total of 758 patients (mean age 51.8 years) were randomized. Adverse events were similar between groups; most common were injection-associated: erythema (84.3%), induration (55.8%), and pruritus (54.9%). There was no significant between-arms difference in DFS events at interim analysis at median follow-up (16.8 months). In the NP-S arm, imaging detected 54.1% of recurrence events in asymptomatic patients versus 29.2% in the placebo arm (P = 0.069). Conclusions: NP-S was well tolerated. There was no significant difference in DFS events between NP-S and placebo. Use of mandated annual scans and image-detected recurrence events hastened the interim analysis contributing to early trial termination.

Labrijn A.F., Janmaat M.L., Reichert J.M., Parren P.W.

The term bispecific antibody (bsAb) is used to describe a large family of molecules designed to recognize two different epitopes or antigens. BsAbs come in many formats, ranging from relatively small proteins, merely consisting of two linked antigen-binding fragments, to large immunoglobulin G (IgG)-like molecules with additional domains attached. An attractive bsAb feature is their potential for novel functionalities — that is, activities that do not exist in mixtures of the parental or reference antibodies. In these so-called obligate bsAbs, the physical linkage of the two binding specificities creates a dependency that can be temporal, with binding events occurring sequentially, or spatial, with binding events occurring simultaneously, such as in linking an effector to a target cell. To date, more than 20 different commercialized technology platforms are available for bsAb creation and development, 2 bsAbs are marketed and over 85 are in clinical development. Here, we review the current bsAb landscape from a mechanistic perspective, including a comprehensive overview of the pipeline. Bispecific antibodies — a large family of molecules that are designed to recognize two different epitopes or antigens — come in many formats and can have the potential for novel functionalities that are not provided by mixtures of monoclonal antibodies. This article reviews the current bispecific antibody landscape from a mechanistic perspective, including a comprehensive overview of the pipeline.

Takegawa N., Tsurutani J., Kawakami H., Yonesaka K., Kato R., Haratani K., Hayashi H., Takeda M., Nonagase Y., Maenishi O., Nakagawa K.

Therapies targeted to human epidermal growth factor receptor 2 (HER2) have proven effective against tumors positive for HER2 amplification, but there is an unmet clinical need for the treatment of tumors that express HER2 protein in the absence of HER2 amplification. [fam-] trastuzumab deruxtecan (DS-8201a) is a novel antibody-drug conjugate composed of the anti-HER2 antibody and the topoisomerase I inhibitor, an exatecan derivative. It has shown efficacy against tumors that express HER2 and is currently under evaluation in clinical trials. We here show that the antitumor activity of [fam-] trastuzumab deruxtecan is dependent on the expression level of HER2 protein in colorectal cancer (CRC) cell lines negative for HER2 amplification. We established isogenic CRC cell lines that express various levels of HER2 protein in the absence of HER2 amplification, and we found that cells that express HER2 at a high level were sensitive to [fam-] trastuzumab deruxtecan but not to conventional HER2-targeted therapies. Furthermore, [fam-] trastuzumab deruxtecan manifested a bystander killing effect both in vitro and in vivo, with cells essentially negative for HER2 expression also being killed in the presence of HER2-expressing cells, an effect that has the potential to overcome heterogeneity of HER2 expression in CRC tumors. Our results thus suggest that [fam-] trastuzumab deruxtecan warrants further study as a potential treatment for CRC tumors that express HER2 protein in the absence of HER2 amplification.

Rugo H.S., Im S., Wright G.L., Escriva-de-Romani S., DeLaurentiis M., Cortes J., Bahadur S.W., Haley B.B., Oyola R.H., Riseberg D.A., Musolino A., Cardoso F., Curigliano G., Kaufman P.A., Pegram M.D., et. al.

1000 Background: Pretreated HER2+ MBC lacks a defined standard of care, although T is commonly used. M has similar HER2 binding and antiproliferative effects as T. By contrast, M’s Fc region is engineered to increase affinity for both alleles of the activating Fc receptor (FcR), CD16A, and decrease affinity for the inhibitory FcR, CD32B. The low affinity CD16A-158F allele (~85% of population) has been associated with diminished clinical response to T. In a Phase 1 trial, M demonstrated acceptable safety, anti-tumor activity, and evidence of HER2-specific antibody and T-cell responses. Methods: SOPHIA (NCT02492711), a randomized, open-label P3 trial, enrolled pts with HER2+ MBC after pertuzumab and 1–3 lines of prior Tx for MBC. Pts were randomized 1:1 to M (15 mg/kg IV q3w + C) or T (6 [8 for loading dose] mg/kg IV q3w + C), stratified by met sites (≤2, > 2), lines of Tx for met disease (≤2, > 2), and C choice (standard dose capecitabine, eribulin, gemcitabine, or vinorelbine). Primary endpoints are central blinded PFS and OS, assessed sequentially using the stratified log-rank test. Objective response rate (ORR) was a secondary endpoint. 257 PFS events were required to provide 90% power to show PFS superiority at 2-sided α = 0.05. Results: Intent-to-treat analysis (536 pts: M 266; T 270) occurred after 265 PFS events. M prolonged PFS over T (median 5.8 vs 4.9 mo, hazard ratio [HR], 0.76; 95% CI, 0.59–0.98; P= 0.033). Treatment effects were more pronounced in pts with CD16A genotypes containing a 158F allele (median PFS 6.9 vs 5.1 mo, HR, 0.68; 95% CI, 0.52–0.90; P= 0.005). In 524 pts with baseline measurable disease (M 262; T 262), ORR was higher with M (22%; 95% CI, 17.3-27.7%) vs T (16%; 95% CI 11.8-21.0%). Safety profiles were comparable in 529 pts who received study therapy. Grade ≥3 AEs and serious AEs occurred in 138 (52%) and 39 (15%) vs 128 (48%) and 46 (17%) pts on M vs T, respectively. PFS data cutoff: 10/10/18. Conclusions: In combination with chemotherapy in pretreated HER2+ MBC, M improves PFS over T with comparable safety. CD16A genotyping suggests a differential benefit in patients with a 158F allele. OS data are maturing. Clinical trial information: NCT02492711.

Clifton G.T., Peace K.M., Holmes J.P., Vreeland T.J., Hale D.F., Herbert G.S., Litton J.K., Murthy R.K., Lukas J., Peoples G.E., Mittendorf Elizabeth A.

The development of HER2-targeted therapy has decreased recurrence rates and improved survival, transforming the natural history of HER2-positive breast cancer. However only a minority of breast cancer patients benefit as these agents are not used in patients with tumors expressing low levels of HER2. Preclinical data suggests a synergistic action of HER2-targeted vaccination with trastuzumab. We report the initial safety interim analysis of a phase II trial that enrolled patients with HER2 low-expressing (IHC 1+/2+) breast cancer who were clinically disease-free after standard therapy. Patients were randomized to receive the HER2-peptide vaccine nelipepimut-S + GM-CSF with trastuzumab (vaccine arm) or trastuzumab + GM-CSF (control arm) and were followed for recurrence. A planned analysis that occurred after enrollment of 150 patients showed no significant differences in toxicity between the two arms, including cardiac toxicity. The clinical efficacy of this combination will be reported 6 months after the final patient was enrolled.

Pondé N., Aftimos P., Piccart M.

Antibody-drug conjugates are an elegant approach to cancer treatment that couples the specificity of monoclonal antibodies to the cytotoxicity of classic chemotherapy agents, permitting, at least in theory, increased activity and reduced toxicity. In breast cancer, the early success of trastuzumab-emtansine (T-DM1) in the HER2-positive metastatic setting led to great hopes, later dashed by results in the early setting (KRISTINE trial) and in combination with pertuzumab (MARIANNE trial). Parallel to this, development of ADCs in breast cancer has suffered other setbacks, including the recent failure of other agents (MM-302) as well as the suspension of a few programs (XMT-1522, ADCT-502) with the overall effect of dampening the impetus of this concept and halting/delaying the progress of drugs associated with it, particularly when immunotherapy is at the center of so many efforts. Numerous antibody-drug conjugates remain, however, in development, and could prove successful. Critically, ADCs could permit the introduction of novel concepts such as the expansion of potent anti-HER2 therapy to HER2-low breast cancer, treatment beyond resistance to T-DM1, and synergy in combination with immune checkpoint blockade. In the early setting, the ATEMPT trial may show that T-DM1 reduces toxicity while maintaining good outcomes for lower risk HER2+ patients. ADCs based on bispecific antibodies are also in development. Finally, breakthroughs are occurring in the orphan triple-negative breast cancer subtype with agents targeting surface proteins. The recent results of Sacituzumab govitecan suggest substantial activity in heavily pre-treated patients and underscore the enduring relevance of antibody drug conjugates as a path towards better outcomes.

Hickerson A., Clifton G.T., Hale D.F., Peace K.M., Holmes J.P., Vreeland T.J., Litton J.K., Murthy R.K., Lukas J.J., Mittendorf E.A., Peoples G.E.

1 Background: Preclinical data shows synergism between trastuzumab (Tz) and HER2-targeted vaccines. We evaluated adjvuant nelipepimut-S (NPS) + GM-CSF with Tz compared to Tz with GM-CSF alone in HER2 low-expressing (LE) breast cancer (BC) patients (pts) to prevent recurrences. After a planned interim analysis showed benefit in triple negative BC (TNBC) pts, the decision was made to close the trial with guidance from the independent DSMB. Here, we report the final analysis of the trial with 7 months (mo) of added follow-up (f/u). Methods: The phase 2b trial enrolled clinically disease-free BC pts after standard therapy. Pts were HLA-A2, A3, A24, and/or A26+, had HER2-LE (IHC 1-2+, FISH non-amplified) BC and were node positive and/or TNBC. Pts were randomized to placebo with GM-CSF(control group, CG) or NPS with GM-CSF (vaccine group, VG), while all received Tz Q3wk for 1 year. GM-CSF or NPS + GM-CSF were given q3wks x 6 starting with the 3rd Tz dose, and boosters every 6 months x 4. Safety was assessed and pts were followed clinically for recurrences. The primary outcome was DFS at 24 mo. Results: 589 pts were screened at 26 sites. 275 pts were enrolled and randomized (VG:136, CG:139). There were no clinicopathologic differences between groups. Concurrent Tz and NPS was safe with no added overall or cardiac toxicity compared to CG and no grade 4/5 toxicities. In the ITT analysis (median f/u 25.7 mo), the estimated DFS was favorable but did not reach significance in the VG compared with the CG (HR 0.62, 95% CI: 0.31-1.25, p = 0.18). In the TNBC pts, the VG had statistically improved DFS compared to the CG (HR 0.26, 95% CI: 0.08-0.81, p = 0.013). Conclusions: The combination of NPS with Tz is safe with no added toxicity compared to Tz alone, even after prolonged exposure (25.7 mo). In this final analysis, there was a trend towards benefit in the ITT population that improved since the interim analysis with added f/u. The significant benefit seen at interim in the TNBC pts continued to strengthen in the VG group. These findings could position the NPS + Tz combination as an adjuvant therapy for early-stage TNBC and warrant further study. Clinical trial information: NCT01570036.

Rinnerthaler G., Gampenrieder S., Greil R.

Since the discovery of the human epidermal growth factor receptor 2 (HER2) as an oncogenic driver in a subset of breast cancers and the development of HER2 directed therapies, the prognosis of HER2 amplified breast cancers has improved meaningfully. Next to monoclonal anti-HER2 antibodies and tyrosine kinase inhibitors, the antibody-drug conjugate T-DM1 is a pillar of targeted treatment of advanced HER2-positive breast cancers. Currently, several HER2 directed antibody-drug conjugates are under clinical investigation for HER2 amplified but also HER2 expressing but not amplified breast tumors. In this article, we review the current preclinical and clinical evidence of the investigational drugs A166, ALT-P7, ARX788, DHES0815A, DS-8201a, RC48, SYD985, MEDI4276 and XMT-1522.

Modi S., Tsurutani J., Tamura K., Park H., Sagara Y., Murthy R., Iwata H., Krop I., Doi T., Redfern C., Moreno-Aspitia A., Redman R., Lee C., Sugihara M., Fujisaki Y., et. al.

Abstract Background: HER2-targeted therapies have improved survival for advanced HER2-positive breast cancers (BC), but none have been approved for tumors with low levels of HER2 expression (ie, HER2 IHC 1+ or 2+/ISH-negative). Trastuzumab deruxtecan (DS-8201a) is a novel HER2-targeted antibody-drug conjugate with a humanized HER2 antibody attached to a potent topoisomerase I inhibitor payload by a cleavable peptide-based linker, which is designed to have broad antitumor activity in HER2-expressing tumors. It has a drug-to-antibody ratio of 7 to 8, a novel linker that is stable in plasma and that is selectively cleaved by lysosomal cathepsins which are upregulated in cancer cells, and its payload has a short systemic half-life. In 2015, a phase 1 study (NCT02564900) was initiated to evaluate the safety and efficacy of DS-8201a in subjects with advanced HER2-expressing or HER2-mutated solid tumors, including HER2-low expressing BC. In this study, the overall confirmed response rate (ORR) in the evaluable subjects was 49.3% (103/209) (April 2018 data cutoff; Iwata H, et al. ASCO 2018). Expanded results from the HER2-low expressing BC subjects are presented here. Methods: This ongoing phase 1 trial included 2 parts. The dose escalation part served to determine the dose-limiting toxicities, the maximum tolerated dose, and to select the recommended dose for expansion (RDE). The dose expansion part further evaluated the safety, tolerability, and efficacy of the DS-8201a at the RDE (5.4 and 6.4 mg/kg; q3wks) in various advanced HER2-expressing or HER2-mutated solid tumors, including heavily pretreated HER2-low BC (IHC 1+ or 2+, ISH-negative). Enrollment of HER2-low subjects is ongoing. Results: At the cutoff date of 18 April 2018, data from 34 HER2-low BC subjects were collected. The median age was 55.8 (range; 33, 75) years, the median number of prior endocrine therapies was 2, and the median number of prior chemotherapies was 3. In this HER2-low BC population, most patients had hormone receptor (HR)-positive disease (85.3%; 29/34); of which 17.2% (5/29) received prior treatment with a CDK4/6 inhibitor. The confirmed ORR was 50.0% (17/34), the disease control rate was 85.3% (29/34), the median time to response was 2.8 (range; 1.2, 13.8) months, the median duration of response (DOR) was 11.0 months, and the median progression-free survival (PFS) was 12.9 months. In the subgroup with HR-positive disease, the ORR was 55.2% (16/29), the median DOR was 11.0 months, and the median PFS was 13.6 months. After exclusion of 8 HER2-low subjects who received prior HER2-targeted therapy, the ORR was 46.2% (12/26). In the overall study, among the 145 BC subjects who received ≥1 dose of DS-8201a (5.4 or 6.4 mg/kg), the most frequent grade ≥3 adverse events included anemia (14.5%), and decreased counts of neutrophils (13.8%) and white blood cells (10.3%). There were 4 fatal cases of interstitial lung disease/pneumonitis in BC subjects, including 2 fatal cases in HER2-low BC subjects. Conclusions: In this study, DS-8201a showed substantial antitumor activity and acceptable safety in heavily pretreated HER2-low BC. Citation Format: Modi S, Tsurutani J, Tamura K, Park H, Sagara Y, Murthy R, Iwata H, Krop IE, Doi T, Redfern C, Moreno-Aspitia A, Redman R, Lee C, Sugihara M, Fujisaki Y, Takahashi S. Trastuzumab deruxtecan (DS-8201a) in subjects with HER2-low expressing breast cancer: Updated results of a large phase 1 study [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-17-02.

von Minckwitz G., Huang C., Mano M.S., Loibl S., Mamounas E.P., Untch M., Wolmark N., Rastogi P., Schneeweiss A., Redondo A., Fischer H.H., Jacot W., Conlin A.K., Arce-Salinas C., Wapnir I.L., et. al.

Background Patients who have residual invasive breast cancer after receiving neoadjuvant chemotherapy plus human epidermal growth factor receptor 2 (HER2)–targeted therapy have a worse prognosis than those who have no residual cancer. Trastuzumab emtansine (T‐DM1), an antibody–drug conjugate of trastuzumab and the cytotoxic agent emtansine (DM1), a maytansine derivative and microtubule inhibitor, provides benefit in patients with metastatic breast cancer that was previously treated with chemotherapy plus HER2‐targeted therapy. Methods We conducted a phase 3, open‐label trial involving patients with HER2‐positive early breast cancer who were found to have residual invasive disease in the breast or axilla at surgery after receiving neoadjuvant therapy containing a taxane (with or without anthracycline) and trastuzumab. Patients were randomly assigned to receive adjuvant T‐DM1 or trastuzumab for 14 cycles. The primary end point was invasive disease–free survival (defined as freedom from ipsilateral invasive breast tumor recurrence, ipsilateral locoregional invasive breast cancer recurrence, contralateral invasive breast cancer, distant recurrence, or death from any cause). Results At the interim analysis, among 1486 randomly assigned patients (743 in the T‐DM1 group and 743 in the trastuzumab group), invasive disease or death had occurred in 91 patients in the T‐DM1 group (12.2%) and 165 patients in the trastuzumab group (22.2%). The estimated percentage of patients who were free of invasive disease at 3 years was 88.3% in the T‐DM1 group and 77.0% in the trastuzumab group. Invasive disease–free survival was significantly higher in the T‐DM1 group than in the trastuzumab group (hazard ratio for invasive disease or death, 0.50; 95% confidence interval, 0.39 to 0.64; P

Peng X., Lan B., Wang J., Li Q., Wang J., Fan Y., Luo Y., Chen S., Mo H., Li L., Sun X., Zhang J., Cai R., Zhang P., Xu B., et. al.

El Gazzah E., Parker S., Pierobon M.

Robbins C.J., Bates K.M., Rimm D.L.

Zhou S., Qin X., Xing W., Xu Z., Wei C., Ren Y., Gong Z.

BackgroundThe efficacy of neoadjuvant therapy (NAT) comprising dual-target drugs has been confirmed among patients with human epidermal growth factor receptor 2 (HER2)-positive breast cancer (BC). Therefore, we explored the differences in responses to NAT and prognosis between patients with HER2(3+) and HER2(2+)/fluorescence in-situ hybridization (FISH)-positive BC after TCbHP-based dual-target NAT.MethodsData from patients with HER2-positive invasive BC who underwent NAT and radical surgery between January 2019 and December 2022 at the Peking University First Hospital and Cancer Hospital of Chinese Academy of Medical Sciences were retrospectively summarized. Propensity score matching (PSM) was used to reduce confounding effects. Pathological complete response (pCR) and invasive disease-free survival (IDFS) were evaluated to respectively reflect therapeutic response and patients’ survival status.ResultsWe selected 132 BC patients (66 pairs) through PSM form a cohort of 308 patients. The pCR rate of patients in the HER2(3+) group was significantly higher than that in the HER2(2+)/FISH-positive group after NAT (P<0.001). Univariate and multivariate logistic regression analyses determined that pCR was significantly affected by tumor grade, hormone receptor (HR) status, HER2 status (P<0.05). The 3-year IDFS rate of HER2(3+) BC patients was better than that of HER2(2+)/FISH-positive BC patient (P=0.083), although the difference was not statistically significant. Furthermore, multivariable Cox regression analysis exhibited that positive lymph node, HER2(3+), and pCR were independent prognostic factors for IDFS.ConclusionHER2(2+)/FISH-positive BC patients exhibited worse treatment response and prognosis than HER2(3+) BC patients after dual-target NAT, indicating that HER2 expression level is a crucial factor influencing the therapeutic efficacy and prognosis of BC patients after TCbHP-based dual-target NAT.

Barco I., González C., García-Font M., Fernández A.G., Fraile M., Tarroch X., Morlius X., Vidal M., González S., Mitru C.B., Vallejo E., Molina G., Torras M., Chabrera C.

Shaaban A.M., Kaur T., Provenzano E.

The concept of binary classification of HER2 status has recently been challenged following the DESTINY-Breast trial data showing a clinically meaningful response to antibody–drug conjugates (ADCs) in invasive breast cancer expressing low levels of HER2. HER2-low breast cancer is defined as an immunohistochemistry (IHC) score of 1+ and 2+ without HER2 gene amplification. While HER2-low breast cancer does not represent a biological entity, it encompasses both hormone receptor-positive and triple-negative breast cancer. Differences exist between this group and HER2-null breast cancer. In this review, we provide an update on HER2-low and HER2-ultralow breast cancer, including background trial data, the evolution of HER2-low expression, current clinical guidelines, quality issues, and future directions.

Li M., Zheng A., Song M., Jin F., Pang M., Zhang Y., Wu Y., Li X., Zhao M., Li Z.

Doucet M., deberti M., Arbion F., Goupille C., Body G., Ouldamer L.

Debbi K., Benderra M.A., Medioni J., Durdux C., To N.H., Boukhobza C., Grellier N., Benmaziane A., Monnier L., Gligorov J., Assaf E., Belkacemi Y.

Shi J., Sun D., Jiang Z., Du J., Wang W., Zheng Y., Wu H.

Torrisi R., Gerosa R., Miggiano C., Saltalamacchia G., Benvenuti C., Santoro A.

Liu S., Du B., Zhou S., Shao N., Zheng S., Kuang X., Zhang Y., Shi Y., Lin Y.

Lian J., Yao R., Pang S., Ren X., Pan B., Zhou Y.

Kou F., Liu H., Zhang Y., Liao X., Hu L., Sun J., Zhang J., Xu Y., Yao L., Xie Y.

PURPOSE Data about the clinical impact of human epidermal growth factor receptor 2 (HER2)–low expression in BRCA1/2 -mutated breast cancer (BC) are limited. This study aimed to clarify the clinical relevance of HER2-low in operable BRCA1/2 -mutated BC. MATERIALS AND METHODS A total of 495 HER2-negative operable BC with germline BRCA1/2 pathogenic variants treated at our institute between October 2003 and September 2020 were included. HER2-low was defined as immunohistochemistry (IHC) 1+ or 2+/fluorescence in situ hybridization–negative, while HER2-zero as IHC 0. Tumor DNA from 25 BRCA1/2 -mutated triple-negative BCs (TNBCs) was subjected to whole-exome sequencing. RESULTS Among the 186 BRCA1 carriers, 38.8% of TNBC (n = 121) and 52.3% of hormone receptor–positive/HER2-negative BC (n = 65) exhibited HER2-low tumors in the BRCA1 subgroup; among 309 BRCA2 carriers, 44.9% of TNBC (n = 49) and 68.1% of hormone receptor–positive/HER2-negative BC (n = 260) exhibited HER2-low tumors in the BRCA2 subgroup. After a median follow-up of 10.9 years (range, 1.23-19.8 years), among BRCA1 -mutated TNBC, HER2-low tumors were significantly associated with better recurrence-free survival (RFS; 10-year RFS: 90.3% v 75.1%; P = .015), distant recurrence-free survival (DRFS; 10-year DRFS: 92.4% v 76.5%; P = .010), and overall survival (OS; 10-year OS: 94.6% v 77.4%; P = .007) than HER2-zero tumors. However, the impact of HER2-low in survival was not observed either in BRCA2 -mutated TNBC or in BRCA1- and BRCA2 -mutated hormone receptor–positive/HER2-negative BC. Notably, BRCA1- mutated TNBC with HER2-low tumors showed higher homologous recombination deficiency scores than those with HER2-zero tumors. CONCLUSION BRCA1 -mutated TNBC patients with HER2-low tumors have a significantly favorable survival, highlighting the possibility of stratifying these patients into two subgroups on the basis of HER2-low status.

Carvalho E., Canberk S., Schmitt F., Vale N.

Breast cancer remains one of the most prevalent diseases worldwide, primarily affecting women. Its heterogeneous nature poses a significant challenge in the development of effective and targeted treatments. Molecular characterization has enabled breast cancer to be classified into four main subtypes: luminal A, luminal B, HER2-positive, and triple-negative breast cancer, based on hormone receptor expression and HER2 status. A deeper understanding of these molecular markers and their associated signaling pathways, such as MAPK and PI3K/AKT, is essential for improving prognosis and optimizing treatment strategies. Currently, several therapeutic agents are utilized in neoadjuvant and adjuvant therapies, often in combination with surgical interventions. However, emerging evidence highlights the growing challenge of drug resistance, which significantly limits the efficacy of existing treatments. Addressing this issue may require innovative approaches, including combination therapies and precision medicine strategies, tailored to the molecular profile of each patient. Therefore, a comprehensive understanding of the pathophysiologic mechanisms driving breast cancer progression and resistance is crucial for the development of advanced targeted therapies with greater precision and efficacy. This review aims to explore recent advancements in molecular research related to breast cancer subtypes and provide a critical analysis of current therapeutic approaches within the framework of precision medicine.