Breast Cancer Mortality and Age at Diagnosis

To the Editor: The study by Dr van de Water and colleagues¹ found that increasing age was associated with higher breast cancer mortality in postmenopausal women with hormone receptor–positive tumors. There are methodological issues in measuring the effect of age on disease-specific mortality.

Classifying patients on the basis of whether there was evidence of breast cancer at the time of their death may be misleading. For instance, if an 80-year-old woman with a known pulmonary metastasis dies, her death will be attributed to breast cancer. However, without a postmortem examination, it is not possible to determine the exact cause of death, which may be due to a non–disease-specific condition such as unstable coronary artery disease. If a 36-year-old woman with breast cancer dies in a motor vehicle crash, it will be impossible without a postmortem examination to definitively determine whether the death is due to the motor vehicle crash or to a complication of her malignancy, such as a pulmonary tumor embolism.²