The primary endpoint was the diagnosis of invasive breast cancer. On each questionnaire, we asked whether breast cancer had been diagnosed and, if so, the date of diagnosis. We search the National Death Index routinely for deaths among women who did not respond to the questionnaires; the last search was conducted in December 2010. We asked all women who reported breast cancer (or next of kin for those who died) for permission to review the pertinent medical records for confirmation. Pathology reports, obtained in 96% of the cases, showed a 99.4% confirmation rate. Carcinomas in situ were excluded. Estrogen- and progesterone receptor (ER/PR) status was abstracted from pathology reports.
