Population-based study of risk factors and metastatic sites in HER2-positive breast cancer with pathological complete response

A pathological complete response (pCR) after neoadjuvant chemotherapy (NACT) is associated with favorable outcomes in patients with HER2-positive early breast cancer; however, brain metastases still occur. A population-based retrospective study using the National Clinical Database-Breast Cancer Registry Japan (2008-2020) included 21,494 patients with HER2-positive early breast cancer who received NACT followed by surgery. After excluding cases without known pCR status or prognostic data, 8421 patients were analyzed: 2430 with pCR and 5991 without pCR. Patients achieving pCR had significantly better 3-year disease-free survival than non-pCR patients. Among pCR cases, hormone receptor status and clinical stage independently predicted recurrence. At 5 years, brain metastases occurred in 2.6% of pCR patients and 4.5% of non-pCR patients. The authors conclude that pCR does not eliminate the risk of brain metastases, highlighting the need for continued vigilance.