Citations

1056 Background: Resistance to HER2-directed therapies remains a major challenge in HER2-positiveMBC. In preclinical models, HER2+ tumors overexpress poly (ADP-ribose) polymerase (PARP), and PARP inhibition induces apoptosis through NF-κB suppression even in the absence of pathogenic mutations in BRCA 1/2 . We evaluated the safety, efficacy, and translational correlates of niraparib combined with trastuzumab in patients (pts) with refractory HER2+ MBC. Methods: This open-label Phase 1b/2 trial (NCT03368729) enrolled pts with HER2+ MBC (IHC 3+ and/or FISH amplified), measurable disease, LVEF ≥50%, and progression on ≥1 prior HER2-targeted therapy; stable CNS disease was allowed. Pts with germline BRCA1/2 mutations or prior PARP inhibitor exposure were excluded. Niraparib 300 mg orally was administered on Days 1–21 of a 21-day cycle with trastuzumab 6 mg/kg IV every 3 weeks (loading dose 8 mg/kg on cycle 1). The Phase 2 portion used a Gehan/Simon two-stage design with early stopping for futility (P0=24%); ≥1 response among the first 20 patients triggered expansion to 40 patients. ORR was assessed by RECIST v1.1, meeting the primary endpoint and allowing response rate estimation with <7% standard error and a two-sided 95% exact CI width of 0.28. Gene expression profiling of paired tumor tissue and peripheral blood mononuclear cells (PBMCs) was performed using the NanoString nCounter Tumor Signaling 360 panel at pretreatment compared to cycle 2. Results: Forty-six pts were enrolled (9/2019–2/2025); 41 were evaluable for response. Pts were heavily pretreated (median 3 prior regimens), including trastuzumab deruxtecan in 22 pts; 33% had brain metastases. Treatment-related adverse events were predominantly grade 1–2 and manageable. Clinical benefit rate (CBR) was 44% (18/41) including 1 complete response, 2 partial responses, and 15 stable disease. Eleven patients achieved disease control ≥ 6 months; 1 patient remained on treatment at data cutoff. Tumor profiling revealed enrichment of a B-cell–driven tertiary lymphoid structure signature with reduced hypoxia signaling in responders. Matched PBMC analyses demonstrated coordinated downregulation of interferon signaling, DNA damage response, metabolic activation, angiogenesis, and resistance pathways in clinical responders, whereas non-responders retained signatures of chronic stress and immune exhaustion. Conclusions: Niraparib plus trastuzumab demonstrated a favorable safety profile and durable clinical benefit in heavily pretreated HER2+ MBC. Integrated tumor and blood-based analyses identify immune-organized tumor microenvironments and systemic immune normalization as key correlates of prolonged response, supporting further investigation of PARP inhibition strategies. Clinical trial information: NCT03368729 .

Abstract Background: In breast cancer, the spatial relationship between immune and tumor cells is increasingly recognized as critical in determining the efficacy of neoadjuvant therapy (NAT). This study investigated how the distribution of immune cells, particularly CD8+ T cells, relative to tumor cells affects treatment outcomes. Methods: Biopsies from 104 breast cancer patients were examined, both pre- and post-NAT, using multiplex immunohistochemistry (mIHC). This study focused on the density and distribution of CD8+ T cells, CD68+ macrophages, FoxP3+ regulatory T cells, and other immune markers. Results: The spatial proximity of CD8+ T cells within 20 µm of cancer cells (N20-CD8+T) was strongly correlated with improved clinical outcomes across diverse tumor subtypes and NAT regimens. A significant post-NAT decrease in CD4+, CD68+, and FoxP3+ cells highlights notable shifts in the tumor immune landscape. A noteworthy finding was the positive correlation between CXCL9 expression and N20-CD8+T cells, suggesting a mechanism for immune cell recruitment and interaction within the tumor microenvironment. These results highlight the complex interplay among NAT, immune cell modifications, and patient outcomes. Conclusions: This study revealed that the proximity of N20-CD8+ T cells to tumor cells is consistently associated with favorable NAT outcomes, transcending tumor subtypes, and treatment differences. This highlights the potential of immune cell dynamics, especially CD8+ T cells, as predictive biomarkers for therapeutic responses in breast cancer, underscoring their vital role in tumor immunity.

4526 Background: Standard methotrexate, vinblastine, doxorubicin and cisplatin (MVAC) demonstrates a survival benefit in the neoadjuvant setting for patients (pts) with muscle invasive bladder cancer (MIBC). Compared with standard MVAC, AMVAC yielded higher response rates with less toxicity in the metastatic setting. Methods: Pts with MIBC, cT2-T4a, and N0-N1 with CrCl >=50 and adequate hepatic and marrow function were eligible. Pts received 3 cycles of AMVAC (methotrexate 30 mg/m2, vinblastine 3 mg/m2, doxorubicin 30 mg/m2, cisplatin 70mg/m2) on day 1, with pegfilgrastim 6 mg day 2 or 3, every 2 weeks. Pts with CrCl < 60 could receive cisplatin split over 2 days. Radical cystectomy (RC) with lymph node dissection was performed 4-8 weeks after the last dose of chemotherapy. Primary endpoint was pathologic complete response (pCR) rate. Results: Accrual is complete with 44 MIBC pts enrolled at 2 institutions (FCCC, TJU) over a 25 month period. Median age 64 (range 45-83). Three withdrew from study early and are not evaluable for response (2 physician discretion, 1 withdrawal of consent). An additional 8 are currently receiving treatment on study with toxicity and response data pending. Of the 33 evaluable pts for whom final data is available, 30 received all 3 cycles of AMVAC at full dose. Three pts received < 3 cycles due to grade 3 fatigue (1), low platelets (1), and disease progression precluding RC (1). 32/33 pts underwent RC, all within 8 weeks of last chemotherapy. Median time from start of chemotherapy to RC was 9.7 wks (range 4.6-13 wks). 13/33 pts (39.4%, 95% CI, 22.7-56.1%) had a pCR. An additional 3 (9.1%) were downstaged to non muscle invasive disease. For the intent to treat cohort (n=36) 8 pts had grade 3-4 AMVAC related adverse events, the most common being anemia (3), fatigue (3) and neutropenia (2) and overall pCR rate was 36.1%. (95% CI, 20.4-51.8%). All pts will have completed study treatment by April 2012. Final results will be presented. Conclusions: Neoadjuvant AMVAC is well tolerated and preliminary results show a pCR rate similar to that reported for standard 12-week MVAC, suggesting that AMVAC for three cycles (6 weeks) is a safe and efficient alternative.