Background: Carcinoembryonic antigen-related cell adhesion molecule 5 (CEACAM5) is a cell-surface glycoprotein highly expressed in several tumor types. This Phase 1, open-label, dose-escalation, dose-expansion study (NCT02187848) investigated SAR408701, a DM4 conjugated ADC targeting CEACAM5, in pts with advanced solid tumors. During dose escalation, maximum tolerated dose (MTD) of SAR408701 was 100 mg/m² IV once every 2 weeks in 14-day cycles. Interim analysis of an ongoing expansion cohort in pts with NSQ NSCLC with CEACAM5 expression in ≥ 50% of the tumor cell population is reported. Methods: SAR408701 was administered at MTD. Primary endpoint: overall response rate (ORR; expansion phase). Secondary endpoints include safety and pharmacokinetics (PK). Tumor assessments were performed every 4 cycles (8 weeks). Results: As of Aug 2, 2018, 22 pts with NSQ NSCLC (21 adenocarcinoma; 1 not yet reported) received SAR408701 at MTD. Median age: 60 years; male: 72.7%; ECOG PS (n = 21): 0 = 38.1%, 1 = 61.9%. Median number of prior anticancer therapies for advanced disease was 3; 66.7% (14/21) received ≥ 3 lines; 59.1% had prior anti-tubulin-based treatments. Pts received a median of 6.5 cycles. 15 pts discontinued due to progressive disease and 1 due to an adverse event (AE; peripheral neuropathy); 6 pts remain on study. ORR was estimated at 22.7% (5/22 pts; 90% CI 11.5–39.9); 40.9% had stable disease. Most frequently occurring all-grade treatment-emergent AEs (TEAEs) were corneal events (40.9%; including keratitis 22.7% [1 Grade 3] and keratopathy 18.2%), dyspnea (31.8%; 5 Grade ≥ 3), asthenic conditions (31.8%) and diarrhea (27.3%). 6 pts had ≥ 1 dose modification due to a TEAE. PK analysis was performed in 14 pts at Cycle 1; mean C_max, AUC, clearance and t_1/2z were 53.1 µg/mL, 297 µg.day/mL, 0.685 L/day and 6.19 days, respectively. Conclusions: In pts with advanced NSQ NSCLC and CEACAM5 expression in ≥ 50% of tumor cells, SAR408701 had a favorable safety profile. Interim analysis of 22 pts achieved the predefined boundary for efficacy (≥ 4 of 30 pts). These data support further development in NSQ NSCLC. Funding: Sanofi Clinical trial information: NCT02187848