Background: A patient's likelihood of dying from breast cancer or another cause can be assessed with competing risks analyses.
Methods: Data for a cohort of 678 patients with primary invasive breast cancer accrued from 1971 to 1990, updated to 1995, included cause of death (e.g., breast cancer vs. other cause). We investigated the effects of age, tumor size, nodal status, ER, PgR, and adjuvant therapy (hormones, chemotherapy, radiotherapy) on type of death and time to death for patients of all ages and for those over the age of 65 years.
Results: Although there were no significant univariate differences in breast cancer death rates by age group (P=0.94), more patients over the age of 65 years died from other causes (41/207 [20%] of those older than 65 years vs. 16/471 [3%] of those younger than 65 years;P<.001). In competing risks analyses, older age was associated with non-breast cancer death, whereas larger tumor size was associated with breast cancer death. PgR was positively, and nodal status negatively, associated with survival, regardless of type. In the older patient group, the competing risks analyses identified similar effects for age and tumor size; in addition, higher ER assay values were less likely to be associated with breast cancer death.
Conclusions: With increased lifespan, there will be more breast cancer cases in women older than 65 years; we have shown that women in this group have more non-breast cancer deaths. It becomes important, then, to delineate differential effects of prognostic factors on competing causes of death.