What is Pathological Complete Response (pCR) in Clinical Trials?

Pathological Complete Response (pCR) is commonly used as a surrogate marker for breast cancer and is defined as the absence of residual invasive cancer in the resected breast tissue and evaluated regional lymph node. This clinical endpoint is often employed for Neoadjuvant Chemotherapy (NACT) trials in breast cancer patients under the FDA's Accelerated Approval Program. In studies following NACT for breast cancer, patients achieving pCR have shown an association with improved Overall Survival (OS) and Event-Free Survival (EFS).