TOP1 and small cell lung carcinoma: Based on preclinical findings where ATR inhibition in combination with a topoisomerase 1 (TOP1) inhibitor demonstrated synthetic lethality, berzosertib and topotecan, a selective TOP1 inhibitor, were evaluated in different solid tumor malignancies [24] and in a proof-of-concept study in patients with small cell lung cancer (SCLC) [25].