Trends in breast cancer-specific death by clinical stage at diagnoses between 2000 and 2017.

Background: Approximately 40 000 individuals die from metastatic breast cancer each year. We examined what fractions of annual breast cancer-specific death are due to stage I, II, III, and IV disease and if these proportions changed over time.

Methods: We used data from Surveillance, Epidemiology, and End Results Program covering 1975-2017. After filtering for female sex at birth, 1 primary tumor type, surgery, American Joint Committee on Cancer Staging Manual (6th edition) stage above 0, no bilateral cancer, and survival data available, the final analysis included 972 763 patients. Temporal trends were assessed using a linear model and analysis of variance test.

Results: The contribution of stage I and II cancers to breast cancer-specific death increased statistically significantly from 16.2% to 23.1% and from 30.7% to 39.5%, respectively, between 2000 and 2017. The contribution of stages III and IV cancers decreased from 36.4% to 30.3% and from 16.7% to 7.1%, respectively. In 2000, 0.92%, 4.0%, and 10.7% breast cancer-specific deaths were due to T1a, T1b, and T1c node-negative cancers, respectively, which increased significantly to 1.9%, 5.8%, and 14.7% by 2017. These temporal trends were similar for hormone receptor-positive and hormone receptor-negative cancers. The contribution of breast cancer-specific death to all-cause mortality declined from 23.9% to 16.6% for stage I and from 47.7% to 36.9% for stage II cancers by 2017.

Conclusions: Patients with stage I and II breast cancers have excellent prognosis, yet these cancers account for more than 60% of current breast cancer-specific death because of their large absolute numbers. To further reduce breast cancer death, strategies are needed to identify and treat patients with stage I and II disease who remain at risk for recurrence.