PURPOSE: Seizure-related homolog protein 6 (SEZ6) is a novel target expressed in small cell lung cancer (SCLC). ABBV-011, a SEZ6-targeted antibody conjugated to calicheamicin, was evaluated in a phase I study (NCT03639194) in patients with relapsed/refractory SCLC. We report initial outcomes of ABBV-011 monotherapy. PATIENTS AND METHODS: ABBV-011 was administered intravenously once every 3 weeks (Q3W) during dose escalation (0.3-2 mg/kg) and expansion. Patients with SEZ6-positive tumors (≥25% of tumor cells with ≥1+ staining intensity by immunohistochemistry) were preselected for expansion. Safety, tolerability, antitumor activity, and pharmacokinetics were evaluated. RESULTS: As of August 2022, 99 patients received ABBV-011 monotherapy (dose escalation, n=36; Japanese dose evaluation, n=3; dose expansion, n=60 [1 mg/kg, n=40]); median age was 63 years (range, 41-79). Thirty-two percent, 41%, and 26% of patients received 1, 2, and ≥3 prior therapies, respectively. The maximum tolerated dose was not reached through 2.0 mg/kg. Most common treatment-emergent adverse events (TEAEs) were fatigue (50%), nausea (42%), and thrombocytopenia (41%). Most common hepatic TEAEs were increased aspartate aminotransferase (22%), increased g-glutamyltransferase (21%), and hyperbilirubinemia (17%); 2 patients experienced veno-occlusive liver disease. Objective response rate (ORR) was 19% (19/98). In the 1-mg/kg dose-expansion cohort (n=40), ORR was 25%; median response duration was 4.2 months (95% CI, 2.6-6.7) and median progression-free survival was 3.5 months (95% CI, 1.5-4.2). CONCLUSIONS: ABBV-011 1.0 mg/kg Q3W monotherapy was well tolerated and demonstrated encouraging antitumor activity in heavily pretreated patients with relapsed/refractory SCLC. SEZ6 is a promising novel SCLC target and warrants further investigation.

The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Small Cell Lung Cancer (SCLC) provide recommended management for patients with SCLC, including diagnosis, primary treatment, surveillance for relapse, and subsequent treatment. This selection for the journal focuses on metastatic (known as extensive-stage) SCLC, which is more common than limited-stage SCLC. Systemic therapy alone can palliate symptoms and prolong survival in most patients with extensive-stage disease. Smoking cessation counseling and intervention should be strongly promoted in patients with SCLC and other high-grade neuroendocrine carcinomas. The "Summary of the Guidelines Updates" section in the SCLC algorithm outlines the most recent revisions for the 2022 update, which are described in greater detail in this revised Discussion text.