In a combined analysis of circulating tumor cells (CTCs) from patients in the ALICE study and the ICON study (a phase 2b trial evaluating immunogenic chemotherapy combined with ipilimumab and nivolumab in patients with metastatic hormone receptor positive HER2− breast cancer), presence of CTCs was associated with poor prognosis: 6 out of 17 CTC-positive patients showed PD-L1 expression, which was associated with significantly shorter OS20. Here, CD274 is linked to breast cancer.