EPCAM and head and neck squamous cell carcinoma: We performed subgroup analysis according to the cancer type (NSCLC, breast cancer, gastrointestinal cancer, genitourinary cancer, HNSCC), CTC enrichment method (EpCAM‐based, size‐based, enrichment‐free), metastatic status (yes, mixed), comparison model (model 1 and model 2), CSV expression (yes, no specified), prognostic cut‐off (≥1 PD‐L1+ CTCs, other cut‐offs), and PD‐L1 detection method (IF, mRNA expression).