Ten-year survival in women with primary stage IV breast cancer.

PURPOSE: To evaluate breast cancer-specific survival at 10 years in patients who present with primary stage IV breast cancer, and to determine whether survival varies with age of diagnosis.

METHODS: We retrieved the records of 25,323 women diagnosed with primary stage IV breast cancer in the surveillance, epidemiology, and end results 18 registries database from 1990 to 2012. For each case, we extracted information on age at diagnosis, tumour size, nodal status, oestrogen receptor status, progesterone receptor status, ethnicity, cause of death and date of death. The Cox proportional hazards model was used to estimate the unadjusted and adjusted hazard ratio (HR) of death due to stage IV breast cancer, according to age group.

RESULTS: Among 25,323 women with stage IV breast cancer, 2542 (10.0 %) were diagnosed at age 40 or below, 5562 (22.0 %) were diagnosed between ages 41 and 50 and 17,219 (68.0 %) were diagnosed between ages 51 and 70. After a mean follow-up of 2.2 years, 16,387 (64.7 %) women died of breast cancer (median survival 2.3 years). The ten-year actuarial breast cancer-specific survival rate was 15.7 % for women ages 40 and below, 14.9 % for women ages 41-50 and 11.7 % for women ages 51 to 70 (p < 0.0001). In an adjusted analysis, the risk of death from breast cancer at 10 years was significantly lower for women ages 40 and below (HR 0.78; 95 % CI 0.74-0.82; p < 0.0001) and for women ages 41-50 (HR 0.82; 95 % CI 0.79-0.85; p < 0.0001), compared to women ages 51-70.

CONCLUSIONS: Approximately 13 % of women with primary stage IV breast cancer survive 10 years after diagnosis. Women diagnosed with stage IV breast cancer before age 50 have better survival at 10 years compared to older women.