Competing cardiovascular and tumor-specific mortality in malignant phyllodes tumor

Malignant phyllodes tumor of the breast is a rare neoplasm, and its long-term competing causes of death remain insufficiently characterized. This study aimed to quantify phyllodes-specific and cardiovascular mortality and determine whether cardiovascular mortality exceeds that expected in the general female population. Women with histologically confirmed malignant phyllodes tumor diagnosed between 2000 and 2020 were identified in the Surveillance, Epidemiology, and End Results (SEER) 17-registry database. Phyllodes-specific, cardiovascular, and other-cause mortality were evaluated using competing-risk methods, while cardiovascular standardized mortality ratios (SMRs) were calculated using United States female circulatory-disease rates and person-time distributed across attained-age strata by Lexis expansion. Among 2106 women followed for a median of 165 months, 294 died from phyllodes-specific causes, 83 from cardiovascular causes, and 163 from other causes. Phyllodes-specific mortality remained the dominant competing risk throughout follow-up, with 180-month cumulative incidences of 14.6% for phyllodes-specific death and 4.4% for cardiovascular death. Cardiovascular mortality was not elevated relative to the general female population when person-time was standardized by attained age (SMR 0.92; 95% confidence interval 0.74-1.14) or additionally by calendar period (SMR 1.00; 95% confidence interval 0.80-1.24). In contrast, assigning all person-time to age at diagnosis produced an inflated SMR of 1.95. Phyllodes-specific death therefore remains the principal long-term mortality risk in malignant phyllodes tumor, whereas the apparent excess cardiovascular mortality results from incorrect person-time allocation rather than a true increase in risk.