Comprehensive Clinical Characterization of Decade-Long Survivors of Metastatic Breast Cancer

SIMPLE SUMMARY: Characterizing features of metastatic breast cancer (MBC) patients with exceptionally favorable prognoses may inform strategies to improve the survival of more typical patients. In this retrospective study, we analyzed clinicopathologic characteristics and treatments of 110 consecutive MBC patients who survived for >10 years. Approximately 70% of patients initially had a single-organ metastasis. The median duration of systemic therapy was 11, 8.4, 7.3, and 0.8 years in the hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2−), HR+/HER2+, HR−/HER2+, and triple-negative breast cancer (TNBC) patients, respectively. Seven HER2+ and ten TNBC patients received <2 years of systemic therapy and remained alive and free of systemic therapy for >10 years. The TNBC subtype and local treatment with curative intent within 1 year of MBC diagnosis were associated with long-term treatment-free survival. Our study suggests that a small subset of patients with HER2+ MBC and metastatic TNBC may be curable with multimodality therapy. ABSTRACT: Background: Elucidating the clinical features of metastatic breast cancer (MBC) patients with an exceptionally favorable prognosis may offer insights to improve the survival of more typical patients. Methods: We collected comprehensive real-world data on clinicopathologic characteristics, treatments, and outcomes of 110 consecutive MBC patients who survived for over ten years from the clinical data warehouse of Samsung Medical Center. Results: The cohort included 54 hormone receptor (HR)-positive/HER2-negative (HR+/HER2−), 21 HR+/HER2+, 16 HR−/HER2+, and 14 triple-negative breast cancer (TNBC) patients. The median age at MBC diagnosis was 48.5 years. Approximately 70% of patients initially had a single-organ metastasis. The most common site of metastasis was the lung (46.4%), followed by distant lymph nodes (37.3%). During a median follow-up of 14.6 years, the median duration of systemic therapy was 11, 8.4, 7.3, and 0.8 years in the HR+/HER2−, HR+/HER2+, HR−/HER2+, and TNBC subgroups, respectively. Seven HER2+ and ten TNBC patients received systemic treatment for less than two years and remained treatment-free for most of the follow-up period, suggesting a potential chance of cure. The TNBC subtype (p < 0.001) and local treatment with curative intent within 1 year of MBC diagnosis (p = 0.002) were significantly associated with long-term treatment-free survival. The survival of HER2+ MBC and TNBC patients, but not that of HR+/HER2− patients, plateaued approximately 13 years after MBC diagnosis. Conclusions: A small subset of patients with HER2+ MBC and metastatic TNBC may be curable with multimodality therapy. Prospective studies integrating clinical and genomic data may identify unique clinicogenomic features of MBC patients who can achieve durable disease control without prolonged chemotherapy.