Lynch Syndrome is an inherited condition involving several well-characterized mutations; MLH1, MSH2, MSH6, and PMS2. Affected families are counselled on their increased risk of numerous malignant diagnoses including colorectal cancer and endometrial cancer, as well as central nervous system malignancies and several other gastrointestinal and genitourinary cancers. Management of Lynch Syndrome includes prevention and surveillance, such as colonoscopies for early detection of colorectal cancer, and prophylactic hysterectomy for endometrial cancer.

There is a suggestion that Lynch Syndrome may confer an increased risk of breast cancer, however the literature remains conflicting. Our work identified an increased risk in MSH2 carrier women in a large Canadian registry (SIR 3.11 (95%CI: 1.95-4.71), lifetime cumulative incidence 22%). Furthermore, we have demonstrated the high penetrance of Lynch Syndrome cancers within their individual family pedigrees, and that similar to other Lynch Syndrome diagnoses, breast cancers occur at a younger age compared to the unaffected Canadian population. Ours is the first study to demonstrate an association between breast cancer risk and family history of Lynch Syndrome-related malignancies, and reports on a large number of breast cancer events compared to many published series.

Identification of breast cancer as a Lynch Syndrome related malignancy could have significant implications for mutation carriers. Effective surveillance and prevention strategies are available and could be further explored. These interventions have proven beneficial in other high-risk populations, such as BRCA1/2 carriers. (By Dr. Mira Goldberg, http://jmg.bmj.com/content/early/2017/08/04/jmedgenet-2017-104542 )