Phase II study of neoadjuvant ipilimumab and nivolumab in combination with paclitaxel following anthracycline-based chemotherapy in patients with treatment resistant stage III triple negative breast cancer (TNBC): BCT1702—Survival results.

608 Background: We examined the efficacy and safety of neoadjuvant ipilimumab and nivolumab combined with paclitaxel following suboptimal response to anthracycline-based chemotherapy in patients with early-stage TNBC. Methods: This single arm phase 2 study enrolled 34 patients at 8 sites. Patients had stage 3 TNBC, after 4 cycles of anthracycline-based therapy, with ≥15mm of tumor remaining or ≥10mm of tumor with ≥1 positive lymph node. A suboptimal response at baseline was defined as <50% reduction in tumor volume after anthracycline-based therapy. Patients received neoadjuvant ipilimumab 1mg/kg IV 6 weekly for 2 doses and nivolumab 240mg every 2 weeks for 6 doses, with weekly paclitaxel at 80mg/m 2 for 12 weeks, followed by surgery. Nivolumab (480mg 4-weekly) continued post operatively for a further 9 months. Primary endpoint was pathological complete response (pCR: ypT0/is, ypN0) in breast and axilla, with secondary endpoints pCR in the suboptimal responders, pCR in PD-L1 positive (≥1% by SP142) or TIL% high (≥30%), event-free (EFS) and overall survival (OS). Results: Between December 2018 and April 2020, 34 patients were enrolled, 33 were evaluable for the primary endpoint. Median age was 46.6yrs. At diagnosis, 97% patients were clinical stage III, 24/34 (70.5%) were clinically node positive, 9/31 (27%) were PD-L1 positive and 6/30 (20%) were TILs% high. At study entry (after anthracycline-based chemo), the median tumor size by ultrasound was 28mm (12-62). The pCR rate was 24.2% (95% CI, 11.09-42.26) in all evaluable, 44.4% 4/9 in PD-L1+ and 9.5% 2/21 in PD-L1- patients. In suboptimal responders, the pCR rate was 25% (95% CI,8.6-49.1) (3/16). At a median follow up of 36.6 months, 9 patients have died. The KM estimates for EFS and OS at 12 months were 96.8% and 93.7%, at 24 months were 84.4% and 84.4% and at 36 months 61.2% and 71.9%, respectively. Patients who achieved a pCR had numerically better EFS (HR 3.61 (0.47-28.2, p=0.2) and OS (HR 2.6 (0.33-21.08); p=0.34). Patients with PD-L1+ tumors vs PD-L1- had a 3-year EFS of 100% vs 52% (p=0.01) and 100% vs 67% OS (p=0.05). Results were similarly favorable for TIL high vs low. Conclusions: The addition of ipilimumab and nivolumab to neoadjuvant chemotherapy resulted in 100% survival for high-risk patients with PD-L1+ and/or TIL% high tumors. Combination CTLA4 and PD-1 targeting agents should be further investigated in Stage 3 TNBC patients. Translational research is ongoing. Clinical trial information: ACTRN12617000651381. Table: see text