Fisch, Samantha

Abstract Introduction: Metaplastic breast cancer (MpBC) is a rare, aggressive subtype of breast cancer that has limited evidence-based data to guide treatment. Historically, MpBC has had limited response to chemotherapy; however, the response of MpBC to antibody-drug conjugates (ADCs) remains poorly characterized. Methods: We performed a retrospective cohort study of patients (pts) with pathologic diagnosis of MpBC who received ADC therapy as part of standard of care in the metastatic setting across 4 NCI-designated cancer centers. The primary endpoints were objective response rate (ORR) at time of best response to ADC & real world PFS (rwPFS) of ADC compared to non-ADC therapy, defined as time from treatment start to time of progression or death. Results: We identified 48 pts with MpBC who received at least one ADC between 3/2016 and 10/2025. Median age was 54 years (range 31-77); all pts were biological females. Most pts had triple negative disease (n=39, 81%), 5 (10%) had HER2+ disease, 3 (6%) had hormone receptor positive disease & 17 (35%) were confirmed HER2-low (IHC 1+ or 2+, ISH nonamplified). The most common MpBC subtypes were with squamous differentiation (n=17, 35%), chondroid (n=11, 23%), matrix-producing (n=11, 23%) & spindle cell differentiation (n=10, 21%). Ten pts (21%) had de novo metastatic disease & 38 (79%) had recurrent disease. Most common metastatic sites were lung (n=33, 69%) & liver (21, 44%). 37/38 (97%) patients had curative intent anthracycline & taxane, with median disease-free interval of 16 months (range 2-241). 18 pts (38%) received curative intent immune checkpoint inhibitor. Most pts received ADC in the first (n=19, 40%) or second line (n=18, 38%) with Sacituzumab govitecan being the most common (n=38, 79%) ADC, followed by Trastuzumab deruxtecan (n=9, 19%). 7 pts (15%) received a second ADC. ORR at time of best response was 38% (n=18), with 4 pts experiencing complete response (1 patient who received ADC in 1L, 3 in the 2L) & 14 experiencing partial response. 3 pts (6%) experienced stable disease, & 27 pts (56%) experienced progressive disease as best response. Median rwPFS of pts receiving ADC in the first line was 2.3 months, compared to 4.3 months in those receiving non-ADC/chemotherapy (HR 1.34; 95% CI 0.72-2.49, p=0.89). Median rwPFS of pts receiving ADC in the second line was 2.6 months, compared to 2.3 months in those receiving non-ADC/chemotherapy (HR 0.56; 0.28-1.11; p=0.10). Toxicity resulted in dose reductions in 17 pts (35%), dose delays in 14 (29%), & ADC discontinuation in 2 (4%). Conclusion: In this multi-institutional cohort of pts with metastatic MpBC, ADC treatment yielded a 38% ORR, including four complete responses. However, rwPFS was poor overall & similar between ADC & non-ADC therapy. These findings highlight the need to develop new treatment strategies for MpBC, though a subset of pts may experience meaningful response to ADC. Citation Format: S. Jacob, S. Premji, S. Fisch, A. LeVee, S. Marion, D. Schmolze, J. Mortimer, L. Huppert, D. Idossa, A. Nayak, P. Wileyto, A. DeMichele, P. D. Shah. Efficacy of antibody drug conjugates in patients with advanced metaplastic breast cancer: a multi-institutional retrospective cohort study [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-09-18.

Abstract Introduction: Metaplastic breast cancer (MpBC) represents a rare subtype, constituting <1% of all breast cancer cases. It is pathologically characterized by epithelial and mesenchymal cellular components exhibiting a basal molecular pattern, hormone receptor and HER2-negativity, and high grade. Clinically, MpBC exhibits an aggressive course with early disease progression and poor survival. Antibody-drug conjugates (ADCs) have been shown to penetrate the central nervous system (CNS); however, little is known about the response of ADCs in MpBC, particularly in patients with CNS disease. Here we aimed to describe features of CNS disease in a subset of patients (pts) who received an ADC for MpBC . Methods: We conducted a multi-institutional retrospective observational study of pts with advanced MpBC treated with ADCs at 4 NCI-designated cancer centers (abstract #A-345). This analysis includes a subset of this cohort with CNS metastases, with the aim of examining the incidence, characteristics, and treatment patterns. Clinical outcomes were evaluated for pts with information available, including CNS median progression-free survival (mPFS; defined from initiation of systemic therapy to time of further documented CNS progression or death) and median real world PFS (rwPFS; defined from time of treatment initiation to documented disease progression or death). Results: We identified 48 pts with MpBC who received an ADC. Among them, we identified 15 (31%) who developed CNS metastases. Of these, the majority (n=11, 73%) had triple-negative breast cancer, and 4 (27%) had HER2-positive breast cancer. The median age was 50 years (32-75 years). The median interval from the initial MpBC diagnosis to CNS metastasis was 13 months (0-54 months). Excluding those with de novo CNS disease, the median interval from time of metastatic diagnosis to development of CNS metastasis [mets] was 3 months (0-22 months). 4 (27%) pts had de-novo metastatic disease, of which 2 (50%) presented with CNS disease. 4 (27%) pts had screening CNS imaging prior to their diagnosis of CNS metastatic disease. At the time of CNS disease diagnosis, 9 (60%) pts had oligometastatic intraparenchymal CNS disease (defined as <5 CNS mets), 5 (33%) had diffuse (>5 CNS mets) CNS disease, and 1 (6%) had leptomeningeal and intraparenchymal disease. Most pts 14(93%) with CNS disease were symptomatic at time of diagnosis. One pt underwent resection, 9 (60%) underwent stereotactic radiosurgery (SRS), 6 (40%) underwent whole brain radiation therapy (WBRT), and 1 pt received intrathecal chemotherapy with methotrexate. The median number of lines in the metastatic setting prior to documented CNS disease was 1 (range 0-3). The majority 13 (87%) underwent a change in systemic therapy at time of CNS disease diagnosis, with 60% changing to an ADC at the time of CNS diagnosis or progression. Among pts with progression of CNS disease warranting change in systemic therapy, the median time from first CNS event to further CNS progression was 6.5 months. Median CNS PFS was 3.5 months (range 1 -74 months) and median rwPFS was 4.4 months. For those patients who used ADCs after diagnosis of metastatic CNS diagnosis (12/15), median rwPFS was 4 months. Conclusions: Within this CNS sub-cohort study, we found that 31% of pts with MpBC developed CNS metastasis. The majority of pts had neurological symptoms at diagnosis, but most pts did not undergo routing screening for CNS disease. Given the high rate of CNS mets within a short timeframe from diagnosis with poor outcomes, CNS screening should be considered. The extremely short median CNS PFS and low median rwPFS of this cohort highlight the guarded prognosis associated with MpBC. Given the small sample size of this cohort, larger studies are warranted to validate these findings. Citation Format: S. Premji, S. Jacob, A. LeVee, S. Marion, S. Fisch, L. Huppert, J. Mortimer, D. Schmolze, A. Nayak, A. DeMichele, P. Shah, R. Leon-Ferre, D. Idossa. Central nervous system disease in patients with metaplastic breast cancer receiving antibody drug conjugates: a multi-institutional study [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-09-07.

1083 Background: T-DXd and SG are both FDA-approved treatments for patients (pts) with HER2-low MBC, but little data exists on the sequential use of these ADCs. Methods: In this multicenter retrospective cohort study, we identified pts with HER2-low MBC treated sequentially with both T-DXd and SG in either order, with or without intervening therapies (IntTx), at 5 academic centers between 2020-2023. We previously reported real-world progression free survival (rwPFS) and real-world overall survival (rwOS) by HR-status and ADC sequence order. Here we provide updated rwPFS and rwOS data, as well as new subgroup analyses by age, sites of disease, and use of IntTx between ADCs for HR- and HR+ disease. Results: 84 pts with HER2-low MBC treated with both T-DXd and SG were included, including 56 pts with HR+/HER2-low MBC (66.7%) and 28 pts with HR-/HER2-low MBC (33.3%). Prior to the start of ADC1, median age was 58 yrs and 22 pts were >65 yrs (26.2%), 65 pts (77.4%) had visceral disease, and 14 pts (16.7%) had central nervous system (CNS) disease. 36 pts (42.9%) had an IntTx between ADCs. Table 1 shows updated rwPFS and rwOS data by HR-status and ADC sequence order. For pts with HR+ and HR- MBC, there was no difference in ADC1 rwPFS or ADC2 rwPFS by age ≤65 vs. >65 yr or by presence vs. absence of visceral disease. For pts with HR- MBC, ADC1 rwPFS and rwOS was shorter for pts with CNS disease vs. pts without CNS disease (rwPFS 5.4 mo (n=6) vs. 8.5 mo (n=22), p=0.03; rwOS 11.6 mo vs. 21.1 mo, p<0.01 respectively). For pts with HR+ and HR- MBC, there was no difference in ADC2 rwPFS with or without receipt of IntTx. There was no difference in time to treatment failure for first IntTx vs. ADC2 if no InTx was given. Conclusions: This is one of the largest multicenter cohorts of pts treated with sequential ADCs for HER2-low MBC. Median rwPFS was longer for ADC1 than ADC2 in all subgroups, regardless of HR-status, ADC sequence order, age ≤65 or >65 yr, presence of visceral disease, or use of IntTx. Among pts with HR-/HER2-low MBC, pts with CNS disease had shorter ADC1 rwPFS and rwOS than pts without CNS disease. [Table: see text]

Abstract Introduction: Interstitial Lung Disease (ILD) is a known adverse event associated with Antibody Drug Conjugates (ADCs), causing fibrosis of the lung. In the DESTINY-Breast 04, TROPICS-02, and ASCENT trials the rate of ILD/Pneumonitis was 12.1%, 0.4%, and 0% respectively. In these studies, the time to first cross-sectional imaging after initiation of ADC was 6 weeks. However, prior treatment with a topoisomerase-1 inhibitor ADC was not permitted in these studies, so the influence of sequential ADC treatments remains unknown. Here, we aimed to characterize the frequency and management of ILD in sequential use of ADCs in a multi-institution retrospective analysis. Methods: We identified patients (pts) with HR+/HER2-low and HR-/HER2-low MBC who had received both Trastuzumab-deruxtecan (T-DXd) and Sacituzumab govitecan (SG) monotherapy (in either order, with or without intervening therapies) who were treated at five academic centers between 2020-2023. Patients had received treatment with the ADC in either routine clinical treatment or as a prior participant on a clinical trial with ADC monotherapy. Information regarding ILD diagnosis, imaging, timing of onset, peak and resolution along with management information was collected and analyzed. Retrospective assessment of ILD toxicity was graded using CTCAE v5.0, based on available clinical and radiographic reports. Results: 10/60 pts who received ADC therapy in this multi-institutional cohort were diagnosed with ILD (all grades). No differences in age or BMI were observed in those who developed ILD versus those who did not, and 9/10 pts were White, 1 was Asian, with a median age of 59 years (47-79 years). Pertinent history in these pts included 3/10 had a prior smoking history, 8/10 had a prior cardiac or pulmonary comorbidity (including sleep apnea, lung cancer, hypertension, hyperlipidemia, thrombosis, or stroke). Prior to receiving their first ADC, 7/10 patients had metastatic disease to the lung. All 10 patients were diagnosed with ILD during treatment with T-DXd. 4 pts initially received T-DXd, then developed ILD and then upon recovery, subsequently received SG. The remaining 6 pts initially received SG (with no reports of ILD), and then received T-DXd and subsequently developed ILD. In the entire cohort, the median time from ADC initiation to first CT scan was 8 weeks (range 1-22 weeks). Within the cohort that developed ILD, the median time from initiation of T-DXd to first CT scan was also 8 weeks (range 6-13 weeks). The median time to diagnoses of ILD was 3 months after initiation of T-DXd (range 0.4-14.5 months). Dyspnea was the most common presenting symptom in 9/10 pts and at diagnosis of ILD, dyspnea was graded as III in 6/10 pts, II in 3/10 pts, and I in 1/10 pts. Diagnostic evaluation included CT chest (9/10), pulmonary consultation (8/10), pulmonary function testing (2/10), and bronchoscopy (1/10). 4/10 patients presented at their highest-grade toxicity at diagnosis. All patients stopped T-DXd treatment, 7 were hospitalized, 7 required supplemental oxygen, and 8 were prescribed steroids for treatment. Of those receiving steroids, the most common starting dose was prednisone 1 mg/kg and doses ranged from 0.5 mg/kg to 9mg/kg prednisone equivalents. No patient received a secondary immunosuppressive agent. The steroid treatment duration ranged from 1-4 months. None of the 10 pts underwent re-challenge with T-DXd and 3/10 developed grade V ILD (death). Conclusion: We observed a 16.6% incidence of all grade ILD (5% grade V ILD) with T-DXd and 0% with SG. In this small cohort study, we did not observe a clear increased risk for ILD with sequential treatment of ADCs. Practice patterns were consistent with recommended diagnostic evaluation and steroid management. Additional strategies are needed to characterize pts most at risk for developing ILD and to identify situations where re-challenge may be safe. Citation Format: Sarah Premji, Laura Huppert, Reshma Mahtani, Samantha Fisch, Naomi Dempsey, Angelina Raimonde-Taylor, Saya Jacob, Laura Quintal, Jo Chien, Michelle Melisko, Ana Sandoval-Leon, Lauren Carcas, Manmeet Ahluwalia, Natasha Harpalani, Jenna Hoppenworth, Dame Idossa, Ruta Rao, Hope Rugo, Karthik Giridhar. Interstitial Lung Disease (ILD) in Sequential Antibody Drug Conjugate (ADC) use in patients with Metastatic Breast Cancer (MBC): A Multi-Institutional experience [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-12-06.

Abstract Introduction. T-DXd is FDA-approved for patients (pts) with hormone receptor positive (HR+) or HR- HER2-low (IHC 1+ or 2+, ISH-) MBC and SG is FDA-approved for pts with HR+/HER2- and triple negative MBC. However, several outstanding questions impact the use of these drugs in clinic, including: 1) what is the efficacy and safety of these agents in real-world populations with diverse pt characteristics not well represented in the pivotal phase III trials, and 2) what is the impact of sequential treatment with ADCs on the efficacy and safety of these agents. Methods. In this multicenter retrospective cohort study, we identified pts with HR+/HER2-low and HR-/HER2-low MBC who had received both T-DXd and SG monotherapy (in either order, with or without intervening therapies) treated at 5 academic centers between 2020-2023. Pts received treatment per standard of care or on a clinical trial with ADC monotherapy. We describe pt demographic and clinical characteristics, treatment history, key safety parameters, and response and survival data by HR+ status and ADC sequence order. Results. Sixty pts with MBC treated sequentially with T-DXd and SG were included in this analysis, including 45 pts with HR+/HER2-low MBC (75.0%) and 15 pts with HR-/HER2-low MBC (25.0%). Most pts were female (n=59; 98.3%), non-Hispanic (n=49, 81.7%), and white (n=43, 71.7%). Median age at start of ADC #1 was 56.6 years (range 23-82). Prior to treatment with ADC #1, most pts had visceral disease (n=45, 75.0%) and 16 (26.7%) had central nervous system metastases. Among pts with HR+/HER2-low MBC, median time from MBC diagnosis to treatment with ADC #1 was 49.0 months, with 4 median lines of prior therapy in the metastatic setting (2 endocrine, 2 chemo). Approximately half of the HR+ pts received T-DXd prior to SG (n=22, 48.9%; median 3.0 prior lines of therapy for MBC, range 1-9) while the other half received SG prior to T-DXd (n=23, 51.1%; median 4.5 prior lines of therapy for MBC, range 1-10). 44% (n=20) received an intervening therapy between ADCs. For HR+ pts who received T-DXd prior to SG, response and survival data is as follows for T-DXd and SG respectively: Overall response rate (ORR) [54.5% and 21.1%], time to next treatment (TTNT) [4.3 mo and 1.6 mo], and real-world overall survival (rwOS) [19.8 mo and 4.9 mo]. For HR+ pts who received SG prior to T-DXd, response and survival data is as follows for SG and T-DXd respectively: ORR [78.3% and 42.9%], TTNT [8.6 mo and 2.8 mo], and rwOS [22.3 mo and 7.3 mo]. Among pts with HR-/HER2-low MBC, median time from MBC diagnosis to treatment with ADC #1 was 8.2 months with 2 median lines of prior therapy in the metastatic setting (2 chemotherapy); 66.7% (n=10) received prior immunotherapy. Most HR- pts received SG prior to T-DXD (n=14, 93.3%) and 40.0% (n=6) received an intervening therapy between ADCs. For HR- pts who received SG prior to T-DXd, response and survival data is as follows for SG and T-DXd respectively: ORR [64.3% and 38.5%], TTNT [6.2 mo and 2.7 mo, and rwOS [15.7 mo and 6.5 mo]. In terms of key safety parameters during treatment with T-DXd, 13.3% of pts (8/60) required a dose reduction. 16.7% (10/60) were diagnosed with interstitial lung disease (ILD)/pneumonitis of any grade including 3 pts with grade 3-4 ILD (5.0%) and 3 pts with grade 5 ILD (5.0%). During treatment with SG, 40.0% of pts (24/60) required a dose reduction. 83.3% (50/60) received growth factor support (24 pts primary prophylaxis; 26 pts secondary prophylaxis); 9 pts (15%) required treatment delay due to neutropenia. Conclusion. This study represents the largest multicenter series to date of pts treated with sequential ADCs for HR+/HER2-low or HR-/HER2-low. ORR was higher and TTNT was longer for ADC #1 than ADC #2 in all subgroups, regardless of HR+ status and ADC sequence order. An additional ~30 pts will be reported at time of final analysis. Future prospective studies are planned to further clarify the efficacy and safety of sequential ADC use and to identify biomarkers of response and resistance. Key demographic, clinical and treatment characteristics in pts with HR+ and HR- HER2-low MBC treated sequentially with T-DXd and SG (in either order, with or without intervening therapies) Abbreviations: T-DXd (trastuzumab deruxtecan), SG (sacituzumab govitecan), MBC (metastatic breast cancer), ADC (antibody drug conjugate), HR (hormone receptor), HER2 (human epidermal growth factor receptor 2), CNS (central nervous system), ET (endocrine therapy), ORR (overall response rate), TTNT (time to next treatment), rwOS (real world overall survival), CI (confidence interval) * Several pts on ADC #2 with ongoing treatment and first scan pending, hence smaller denominator for response assessment Citation Format: Laura Huppert, Reshma Mahtani, Samantha Fisch, Naomi Dempsey, Sarah Premji, Angelina Raimonde-Taylor, Saya Jacob, Laura Quintal, Jo Chien, Michelle Melisko, Ana Sandoval-Leon, Lauren Carcas, Manmeet Ahluwalia, Natasha Harpalani, Jenna Hoppenworth, Dame Idossa, Ruta Rao, Karthik Giridhar, Hope Rugo. Multicenter retrospective cohort study of the sequential use of the antibody-drug conjugates (ADCs) trastuzumab deruxtecan (T-DXd) and sacituzumab govitecan (SG) in patients with HER2-low metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS08-04.