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

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

Methods: We used data from SEER covering 1975 to 2017. After filtering for female sex at birth, one primary tumor type, surgery, AJCC (6th edition) stage > 0, no bilateral cancer, and survival data available, the final analysis included 972,763 patients. Temporal trends were assessed using a linear model and ANOVA test.

Results: The contribution of stage I and II cancers to BCSD increased 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%. In 2000, 0.92%, 4.0% and 10.7% of BCSD were due to T1a, T1b, and T1c node-negative cancers which increased significantly to 1.9%, 5.8%, and 14.7% by 2017. These temporal trends were similar for hormone receptor-positive and -negative cancers. The contribution of BCSD 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/II breast cancers have excellent prognosis, yet these cancers account for over 60% of current BCSD because of their large absolute numbers. To further reduce breast cancer death strategies are needed to identify and treat patients with stage I/II disease who remain at risk for recurrence.