Breast cancer in Irish families with Lynch syndrome

1543 Background: Breast cancer is not among the recognised malignant manifestations of Lynch Syndrome which include colorectal, endometrial, gastric, ovarian and upper urinary tract tumours. In this study we report the prevalence of breast cancer in Irish Lynch Syndrome families and determine immunohistochemical (IHC) expression of mismatch repair proteins (MMR) in available breast cancer tissue. Methods: Breast cancer prevalence was determined among Lynch Syndrome kindreds from two institutions in Ireland. One kindred was omitted due to a biallelic MMR and BRCA1 mutation.The clinicopathological data that was collected on breast cancer cases included age of onset, morphology, and hormone receptor status, and a genotype phenotype correlation was investigated. Immunohistochemical staining was performed for MLH1, MSH2, MSH6, and PMS2 on all available breast cancer tissue from affected individuals. Results: The distribution of MMR mutations seen in sixteen pedigrees were as follows; MLH1 (n=5), MSH2 (7), MSH6 (3), PMS2 (1). Sixty cases of colorectal cancer and 14 cases of endometrial cancer were seen. Seven breast cancers (5 invasive ductal and 2 invasive lobular cancers) and 1 case of ductal carcinoma in situ were reported in 7 pedigrees. This compared with 4 cases of prostate cancer. Of the 7 LS kindreds containing breast cancer, 6 MSH2 mutations and 1 MSH6 mutations were identified. Median age of breast cancer diagnosis was 49 years (range 38-57). Hormone receptor status is available on 3 breast cancer cases at time of abstract submission; all were ER positive and HER 2 negative. All cases had grade 2 or 3 tumours. 5 samples were available for IHC evaluation. 3 out of 5 cases showed loss of MMR expression, all showed loss of MSH2 and MSH6 expression. One of the two cases with normal IHC expression in breast tissue belonged to a kindred where 3 siblings with colorectal cancer and documented deleterious mutations demonstrated no IHC loss. Conclusions: Breast cancer occurred at an early age and was more common than prostate cancer in Irish Lynch Syndrome pedigrees. All identified breast cancer were in kindreds with MSH2 or MSH6 mutations. Enhanced breast cancer screening may be warranted in certain Lynch Syndrome kindreds.