42606 Genetic Referral and Diagnosis of Lynch Syndrome in Patients with Cutaneous Sebaceous Lesions

Background: Immunohistochemistry (IHC) in cutaneous sebaceous lesions (SL) evaluating for loss of mismatch repair protein expression can be used to screen patients for Lynch syndrome (LS), an inherited cancer predisposition syndrome. The phenotypic variant of LS associated with both cutaneous and visceral findings is historically referred to as Muir-Torre syndrome (MTS). There is little data on rates of genetic referral and outcomes of genetic testing within this cohort. The aim of our study is to describe the utility of IHC and characterize outcomes of genetics referrals and testing in patients with SL. Retrospective chart reviews were performed for patients with a pathology-confirmed diagnosis of SL between January 2009 and December 2019. 447 patients with 473 SL were identified. Excluding 20 patients with known LS, IHC was conducted in 173 (41%) patients. 92/173 (53%) patients had abnormal results. 69/92 (75%) patients were referred to genetics. 32 additional patients were referred with normal IHC (n=22) or without IHC (n=10). Of 101 patients referred, 65 (64%) were seen and 47 (47%) completed genetic testing. 7/47 (15%) had pathogenic variants associated with LS, with six having concordant abnormal IHC and one without IHC. Cancer genetics referral of patients with SL, particularly for lesions with abnormal IHC, yields a significant rate of LS diagnosis. Providers should consider genetics referral for patients with SL with abnormal IHC and/or personal or family history of cancers suggestive of LS.