Young-onset breast cancers tend to be more aggressive than later-onset tumors and may have different risk factor profiles. Among young-onset cases, there may also be etiologic differences between ductal carcinomas in situ (DCIS) and invasive breast cancer, particularly if some factors promote malignant transformation. Researchers evaluated the association between several potential risk factors and young-onset breast cancer in the Two Sister Study (2008-2010), a sistermatched case-control study involving 1,406 women diagnosed with breast cancer before age 50 (1,185 invasive, 221 DCIS) and 1,648 controls. Older age at menarche, younger age at menopause, premenopausal hysterectomy, early age at first-term pregnancy, obesity, and consumption of alcohol were associated with reduced risk of young-onset breast cancer. These patterns remained when the analysis was limited to invasive breast cancers. In general, effect estimates were similar for youngonset invasive breast cancer and DCIS, although the number of DCIS cases was small. The researchers conclude that in this sister-matched case-control study of young-onset breast cancer, many of the studied risk factors were associated with young-onset invasive breast cancer. There were few discernable differences in risk factors for young-onset DCIS versus young-onset invasive breast cancer.
Source: Risk factors for young-onset invasive and in situ breast cancer. K.M. O'Brien, J. Sun, D.P. Sandler, L.A. DeRoo, C.R. Weinberg. Cancer Causes Control, 2015 Sep 25.