Background: Lurbinectedin, a selective inhibitor of oncogenic transcription, received accelerated approval from the US FDA in June 2020 as monotherapy (3.2 mg/m² IV every 21 days) for adults with metastatic SCLC with disease progression on or after platinum-based chemotherapy. This approval was based on the overall response rate (35.2%) and duration of response (DOR; 5.3 months) observed in 105 patients from a phase 2 trial. The ATLANTIS trial (NCT02566993) investigated the combination of lurbinectedin 2.0 mg/m² IV + doxorubicin (DOX) 40.0 mg/m² IV versus topotecan or CAV. This post hoc analysis explored the efficacy and safety of single-agent lurbinectedin in patients who completed 10 cycles of the combination and then switched to lurbinectedin monotherapy per protocol. Methods: Eligible patients were ≥18 years of age with limited-stage or extensive-stage SCLC, 1 prior line of platinum-based chemotherapy (PD-1/PD-L1 inhibitors were also permitted), ECOG PS ≤2, and chemotherapy-free interval ≥30 days. Tumor assessments were per an independent review committee (IRC). Results: Patients who completed 10 cycles of lurbinectedin + DOX and switched to lurbinectedin monotherapy (n = 50) had a median age of 61.5 years (range: 43, 77); 62% were male; and 100% had an ECOG PS < 2. The overall median number of cycles was 15 (range: 11, 47) and included a median of 5 (1, 37) cycles on monotherapy. The majority of patients who switched to lurbinectedin monotherapy maintained or improved their tumor response (Table). All 3 patients who achieved a complete response (CR) on combination therapy maintained their CR on monotherapy. Of the 26 patients with a partial response (PR) on combination therapy, 3 (12%) achieved a CR and 15 (58%) maintained their PR. Of the 19 patients with stable disease (SD) on combination therapy, 3 (16%) improved from SD to PR (n = 2) or CR (n = 1) and 8 (42%) maintained SD. The median DOR was 8.3 months (95% CI: 7.1, 11.0). The median overall survival (OS) was 20.7 months (95% CI: 15.7, 24.8). Grade 3/4 hematologic abnormalities based on laboratory assessment included lymphopenia (36%), anemia (16%), thrombocytopenia (12%), neutropenia (12%), and leukopenia (10%). Febrile neutropenia was reported in 4% of patients. Conclusions: Patients with relapsed SCLC in ATLANTIS who completed 10 cycles of lurbinectedin + DOX combination and switched to lurbinectedin monotherapy tended to maintain or improve their tumor response (including an increase in CRs), with favorable OS and DOR and acceptable tolerability with no new safety signals. Clinical trial information: NCT02566993.

PD, progressive disease. ^a41 patients at 3.2 mg/m², 3 patients at 2.6 mg/m², and 6 patients at 2.0 mg/m². ^b2/50 patients did not have a tumor assessment on monotherapy per IRC.