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The Two Sister Study: A Family-Based Study of Genes and Environment in Young-Onset Breast Cancer

To study environmental and genetic causes of young onset breast cancer, we recruited women who had been young when recently diagnosed (under age 50 and within 4 years of enrollment), and had been identified as potentially eligible by a sister who was already participating in the ongoing Sister Study. The unaffected sister had already provided consent, questionnaire-based information and DNA (blood-based) when she enrolled in the Sister Study. Her case sister then provided comparable questionnaire-based information and DNA via a mail-back saliva collection kit. To enable family-based analyses, parents were also asked to (only) provide consent and a saliva sample. Because the cases were young-onset, most parents were alive, but unavailability of the parents was not a basis for exclusion. The study was funded in part by Susan G. Komen for the Cure.