Complete remission in metastatic breast cancer: expecting the unexpected-results of a cross-sectional study

Complete response (CR) in metastatic breast cancer (MBC) is rare. This study aims at analyzing the characteristics and outcome of MBC patients achieving CR. We performed a cross-sectional analysis of clinical data from a consecutive series of MBC patients admitted at the Division of Medical Oncology of Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy, achieving CR following treatment for systemic disease and with at least 2 years of follow-up. Seventy-six MBC patients with CR were identified during a calendar year. 47 patients (61.8%) achieved CR more than once, for a total of 123 cases. Median age at MBC diagnosis was 56 years (range 30-76). 52 patients (68.4%) presented with recurrent disease, 24 (31.6%) with de novo metastatic disease. The majority of patients (80.3%) had hormone receptor (HR) positive and 26 (34.2%) had HER2 overexpressing MBC. 54 patients (71.1%) had only one site of metastatic disease. 33 patients (43.4%) received a local approach as part of their treatment and 67 (54.5%) achieved CR during maintenance therapy. CRs were durable, as after a median follow-up of 8.3 years (interquartile range 5.8-11.0 years) 42 patients (55.3%) were alive with no evidence of disease. Durable CRs can occur after systemic therapy alone or after combined systemic and local treatments. Most cases presented CR in the presence of limited disease spreading, not necessarily on first-line therapy. Our study highlights the crucial role of multidisciplinary approach to MBC and the benefit of maintenance treatment.