This is a multicenter, open label, phase 1/2 basket trial to evaluate the efficacy and safety of olaparib (PARPi) in combination with durvalumab (anti-PD-L1 mAb) in 264 patients with advanced solid tumors, which include metastatic and HER2-negative breast cancer containing germline BRCA mutation (gBRCAm), relapsed ovarian cancer with gBRCAm, relapsed small cell lung cancer (SCLC), and gastric cancer (initial stage cohorts). Here, ERBB2 is linked to ovarian cancer.