Metastatic breast cancer in young women: a population-based cohort study to describe risk and prognosis.

Abstract

There is limited information on the risk of metastatic breast cancer (MBC) to inform younger women, particularly those under 40 years. We conducted a retrospective analysis of a population-based cohort study to describe the risk, site and prognosis of MBC in young women under 40 years with an initial diagnosis of non-metastatic breast cancer and compared with older women. Data were extracted from the New South Wales Central Cancer Registry and the Admitted Patient Data Collection database between 2001-2007. Main outcome measures were 5-year cumulative incidence of MBC, prognostic factors for MBC and overall survival (OS) from the date of MBC diagnosis. Three hundred and ninety-five (6%) of 6640 women with non-metastatic BC were <40 years. The 5-year cumulative incidence of MBC was 24% (95% CI 20-29%) for women <40 years with non-metastatic BC, compared with 9% (95% CI 9-10%) for women ≥40 years. Significant independent risk factors for MBC ≤ 5 years were age <40, regional disease at diagnosis, low socioeconomic status and the presence of other non-breast primary. At first record of MBC, visceral sites were more common for women <40 years than ≥40 (54% vs 43%; P = 0.03). Median survival for women with MBC within 5 years was not significantly different between young and older women (<40 years 18 months vs ≥40 years 14 months; log-rank P = 0.21). Women with non-metastatic BC before age 40 have a higher 5-year risk of developing MBC than older women. There were no significant differences in median survival following MBC between young and older women.