Background: E7389-LF is a liposomal formulation of the microtubule dynamics inhibitor eribulin. Combining E7389-LF with an immune checkpoint inhibitor (ICI; eg, nivolumab) may improve antitumor response via vascular remodeling. The phase 1b part of the open-label Study 120 evaluated the dosing and safety of E7389-LF in combination with nivolumab in patients (pts) with solid tumors. The phase 2 part assessed efficacy and safety in disease cohorts; herein, we report results from the SCLC cohort. Methods: Pts with unresectable and measurable SCLC who had progression during or after 1^st-line (1L) platinum-based chemotherapy with/without an ICI were enrolled to the SCLC cohort of the phase 2 part of Study 120. Pts received E7389-LF 2.1 mg/m² in combination with nivolumab 360 mg IV Q3W. The primary objective of the phase 2 part was to assess the objective response rate (ORR). Secondary objectives included assessments of safety and progression-free survival (PFS); exploratory objectives included the disease control rate (DCR), overall survival (OS), and biomarker analysis. Tumor response was assessed by investigators per RECIST v1.1 Q6W. All adverse events (AEs) were monitored and recorded. Results: In the SCLC cohort, 34 pts were enrolled; the median age was 66.0 years (range 46–81). At data cutoff (May 31, 2022), 5 pts (14.7%) were undergoing treatment. Discontinuations occurred in 29 pts (85.3%)—26 (76.5%) primarily due to disease progression, 3 (8.8%) due to an AE. Efficacy analyses included 33 pts, as 1 pt had their diagnosis of SCLC changed to a different cancer type after being enrolled. Of the 33 evaluable pts, 27 (81.8%) had an ICI as part of their prior 1L therapy. The ORR of E7389-LF in combination with nivolumab was 24.2% (95% CI 11.1–42.3) in the evaluable population; the DCR was 75.8% (95% CI 57.7–88.9). Median PFS was 3.98 mos (95% CI 2.63–4.40); the 6-mo PFS rate was 27.7% (95% CI 13.0–44.6). At a median follow-up period of 10.6 mos, median OS was not reached (95% CI not estimable); the 6-mo OS rate was 90.9% (95% CI 74.4–97.0). Treatment-related, treatment-emergent (TE)AEs of any grade and of grade ≥3 severity occurred in 97.1% (n = 33) and 82.4% (n = 28) of the 34 enrolled pts, respectively; the most common treatment-related TEAE was neutropenia (any grade: 58.8% [n = 20]; grade ≥3: 52.9% [n = 18]). The neutrophil count nadir occurred around cycle 1 day 8. TEAEs led to dose reduction of E7389-LF in 19 pts (55.9%). Withdrawal of E7389-LF or nivolumab occurred in 5 pts (14.7%): acute kidney injury, cough, myocarditis, pneumonitis, and radiation pneumonitis (n = 1 each). Changes in vascular and immune-related plasma markers were observed. Conclusions: E7389-LF in combination with nivolumab showed notable antitumor activity as 2L therapy in pts with SCLC, as evidenced by the notable ORR of 24.2%. No new safety signals were observed for this combination. Clinical trial information: NCT04078295.