Limited M1 disease: a significant prognostic factor for stage IV breast cancer

The prognosis of patients with breast cancer presenting with distant metastasis can vary depending on disease extent. This study evaluates a definition of limited M1 disease in association with survival in a cohort of women presenting with metastatic breast cancer.

The study cohort comprised 692 women referred to the BC Cancer Agency between 1996 and 2005 with M1 breast cancer at presentation. Limited M1 disease was defined as <5 metastatic lesions confined to one anatomic subsite. Extensive M1 disease was defined as ≥ 5 lesions or disease in more than one subsite. Clinicopathologic and treatment characteristics and overall survival (OS) were compared between subjects with limited (n = 233) versus extensive (n = 459) M1 disease. Multivariable analysis was performed by Cox regression modeling.

Median follow-up time was 1.9 years. Five-year Kaplan-Meier OS was significantly higher in patients with limited compared to extensive M1 disease (29.7 vs. 13.1 %, p < 0.001). In the multivariable Cox regression analysis, limited M1 disease was significantly associated with OS (hazard ratio 0.51, 95 % confidence interval 0.40-0.66, p < 0.001). The only patient subsets with limited M1 disease with poor 5-year OS <15 % were patients with Eastern Cooperative Oncology Group performance status of ≥ 2 or estrogen receptor-negative status.

Limited M1 disease, defined as <5 metastatic lesions confined to one anatomic subsite, is a relevant favorable prognostic factor in patients with stage IV breast cancer. This definition may be used in conjunction with other clinicopathologic factors to select patients for more aggressive systemic and locoregional treatments.