Background: DS-1062a is a trophoblast cell-surface antigen 2 (TROP2)-targeting antibody drug conjugate. TROP2 is highly expressed in epithelial cancers, including non-small cell lung cancer (NSCLC). Overexpression of TROP2 may be associated with poor survival in some solid tumors. Preclinical studies showed promising antitumor activity of DS-1062a in mouse models with TROP2-positive tumors. Preliminary results are reported in the dose escalation part of this phase 1 study. Methods: This is an ongoing phase 1 study of DS-1062a in patients (pts) with advanced solid tumors in the US and Japan (NCT03401385). Adult (age ≥20 years in Japan or ≥18 years in US) pts with measurable disease per RECIST v1.1 and sufficient tumor tissue sample for TROP2 measurement were eligible. Pts were excluded if they had multiple primary malignancies or untreated brain metastases. Endpoints included safety, pharmacokinetics, and efficacy. Results: As of November 16, 2018, 22 pts with advanced NSCLC were treated with DS-1062a at doses of 0.27-mg/kg (n = 4), 0.5-mg/kg (n = 5), 1.0-mg/kg (n = 7), and 2.0-mg/kg (n = 6). Overall, mean (standard deviation) treatment duration and cumulative dose were 7.8 (4.1) weeks and 181.8 (141.4) mg, respectively, with a median of 2 (range 1–6) cycles initiated. The majority (n = 18; 81.8%) of pts had ≥1 treatment-emergent adverse event (TEAE). The most common TEAE, fatigue (n = 9), was the only grade ≥3 treatment-related TEAE (n = 1; 2.0-mg/kg). Serious TEAEs, reported in 5 pts in the 0.27-mg/kg (n = 2), 0.5-mg/kg (n = 2), and 2.0-mg/kg (n = 1) cohorts, were not treatment-related. TEAEs leading to discontinuation occurred in 1 pt in the 0.27-mg/kg cohort (pleural effusion; not treatment-related). One pt died due to progressive disease. Peak concentration (C_max) and area under the curve from time 0 to last measurable concentration (AUC_last) increases were generally dose proportional. Of 18 tumor evaluable pts, 1 had a partial response (PR; 1.0-mg/kg), and 8 had stable disease (SD). Conclusions: DS-1062a was well tolerated at doses up to 2.0-mg/kg. An observable PR and multiple pts with SD warrant further evaluation of DS-1062a. The maximum tolerated dose has not been reached, and this study is ongoing. Clinical trial information: NCT03401385