Berzosertib + Topotecan in Relapsed Platinum-Resistant Small-Cell Lung Cancer (DDRiver SCLC 250)

Inclusion Criteria

• Dose level 1 participants with histologically proven advanced solid tumors, for which no effective standard therapy exists, or standard therapy has failed or cannot be tolerated
• Dose level 1 participants with Eastern Cooperative Oncology Group Performance Status (ECOG PS) less than or equal to ( =) 70 percent (%)
• Dose level 2 and main part participants with ECOG PS = 60%
• Dose level 2 and main part participants with histologically confirmed SCLC
• Dose level 2 and main part participants with radiologically confirmed progression after first-line or chemoradiation platinum-based treatment (carboplatin or cisplatin), with or without immunotherapy, for treatment of limited or extensive stage SCLC, with a Platinum-free interval (PFI) less than ( =] Class III), unstable angina pectoris, myocardial infarction, uncontrolled cardiac arrhythmia, cerebral vascular accident/stroke. Calculated corrected QT interval (QTc) average (using the Fridericia correction calculation) of greater than [>] 450 millisecond (msec) for males and > 470 msec for females. Any psychiatric illness/social situations that would limit compliance with study requirements
• Unstable brain metastases; however, participants with known brain metastases may be enrolled in this clinical study if they are clinically stable (without evidence of progression by imaging for at least 2 weeks prior to the first study intervention dose and any neurologic symptoms have returned to baseline), have no evidence of new brain metastases, and are on a stable or decreasing dose of steroids for at least 14 days prior to study intervention Participants with carcinomatous meningitis are excluded regardless of clinical stability. Screening central nervous system imaging is not mandatory
• Prior malignant disease within the last 3 years. Exceptions include fully resected basal cell carcinoma of the skin or squamous cell carcinoma of the skin, in situ cervical cancer, fully resected ductal carcinoma in situ of the breast, superficial or noninvasive bladder cancer, and Stage IA, Grade I endometrioid endometrial cancer with no myometrial invasion, that has undergone curative therapy. Participants with other localized malignancies treated with curative intent need to be discussed with the Medical Monitor
• Participants not recovered from adverse events (AEs) Grade > 1 from prior anticancer therapies, including surgeries. Exception: Grade 2 AEs not constituting a safety risk (for example [e.g.], alopecia), based on the Investigator's judgment; must consult with the medical Monitor prior to enrollment.
• Other protocol defined exclusion criteria could apply