CD274 and breast cancer: Pre‐treatment PD‐L1+ CTCs were associated with inferior PFS in breast cancer (HR = 1.90, 95% CI 1.24–2.91) and genitourinary cancer (HR = 4.81, 95% CI 2.02–11.45), predicted significantly worse OS in breast (HR = 2.62, 95% CI 1.50–4.59), and gastrointestinal cancer (HR = 3.29, 95% CI 2.06–5.26), respectively.