Unanticipated and extremely high screen failure rate. There was no evidence of safety concerns in the study.

This study evaluates KRT-232, a novel oral small molecule inhibitor of MDM2, for the treatment of patients with relapsed or refractory small cell lung cancer.

This study will be conducted in 2 parts. Part 1 will evaluate two treatment arms, each with a different KRT-232 dose. Part 2 will continue the evaluation of the selected treatment arms from Part 1.

Inclusion Criteria:

• Histologically or cytologically confirmed diagnosis of SCLC documented as TP53WT
• Disease must be measurable per RECIST Version 1.1
• Evidence of radiographic progression during or after at least one prior platinum-containing therapy with no curative therapy available. Subjects who have received only one prior line of therapy must not be candidates for platinum-based regimens at relapse.
• Subjects must have received a checkpoint inhibitor (PD-1 or PD-L1) unless contraindicated if checkpoint inhibitors are approved and available.
• ECOG ≤ 2

Exclusion Criteria:

• Symptomatic or uncontrolled central nervous system (CNS) metastases.
• Prior treatment with MDM2 inhibitors
• Chemotherapy, immune therapy, cytokine therapy, or any investigational therapy within 14 days prior to the first dose of study treatment
• Grade 2 or higher QTc prolongation (> 480 milliseconds per NCI-CTCAE criteria, version 5.0)
• History of major organ transplant