Author Affiliations: Department of Biostatistics, Hôpital Saint-Louis, Paris, France (firstname.lastname@example.org).
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
Biau DJ, Porcher R. Breast Cancer Mortality and Age at Diagnosis. JAMA. 2012;307(19):2023-2024. doi:10.1001/jama.2012.3613