Background: As monotherapies, both ERI (a chemotherapeutic microtubule inhibitor) and PEMBRO (a programmed death [PD]-1 blocking immunotherapy) have shown promising antitumor activity in mTNBC. Emerging data suggest that the addition of immunotherapy to traditional chemotherapy holds promise for mTNBC. This open-label, single-arm, phase 1b/2 study evaluated the safety and efficacy of ERI + PEMBRO in mTNBC. Methods: Patients (pts) with mTNBC and ≤2 prior systemic anticancer therapies for metastatic disease were enrolled and stratified by prior number of therapy (Stratum 1, 0; Stratum 2, 1–2). Pts received IV ERI 1.4 mg/m² on day (d)1 and d8 and IV PEMBRO 200 mg on d1 of a 21-d cycle. The primary objectives were safety and objective response rate (ORR per RECIST 1.1 by independent imaging review). Assessments also included efficacy outcomes by PD ligand-1 (PD-L1) expression status; PD-L1+ was defined as a combined positive score ≥1 using the PD-L1 IHC 22C3 pharmDx. Results: As of data cutoff (July 31, 2019), 167 pts (Stratum 1, n=66; Stratum 2, n=101) were enrolled and treated. No dose-limiting toxicities were observed. The most common treatment-emergent adverse events were fatigue (66%), nausea (57%), peripheral sensory neuropathy (41%), alopecia (40%), and constipation (37%). No deaths were considered treatment related. The overall ORR was 23.4% (95% CI: 17.2–30.5). Efficacy outcomes by PD-L1 status (PD-L1+, n=74; PD-L1-, n=75) and stratum are presented (table). Conclusions: ERI + PEMBRO has activity in pts with mTNBC. There was a trend toward more robust activity for the combination among patients with PD-L1+ tumors compared to PD-L1- tumors in the first-line setting (Stratum 1); whereas, in the later-line setting (Stratum 2) similar survival outcomes were observed among the PD-L1+ and PD-L1- pts. ERI + PEMBRO shows promise for mTNBC with efficacy that appears greater than historical reports of either agent alone. Clinical trial information: NCT02513472.

^aExcludes 18 patients who had unknown tumor PD-L1 status. DOR, duration of response; m, median; NE, not evaluable; OS, overall survival; PFS, progression-free survival.