Improving detection of Lynch syndrome using a reflex immunohistochemistry algorithm for all patients with newly diagnosed colorectal cancer.

Abstract

98 Background: Identifying patients with Lynch syndrome has profound impact on the clinical care of patients and their families. Previous guidelines based on family history alone have shown low sensitivity. In our medical center, the detection rate of Lynch syndrome was <1% among colorectal cancer cases. Methods: We have developed a system-based algorithm using centralized testing by immunohistochemistry (IHC) for four mismatched repair (MMR) proteins (MLH1, MSH2, MSH6, and PMS2) as a screening method for all newly diagnosed colorectal cancer patients, followed by step wise testing of BRAF mutation, MLH1 promoter hypermethylation, +/- microsatellite instability, and germline mutation. Results: From April 1, 2011, to July 11, 2012, we have screened 116 patients. IHC detected absent expression of at least one of the MMR proteins in 18 cases. Three cases showed missing expression of MSH2/MSH6 and the presence of a germline mutation in MSH6 was confirmed in two cases. The newest case is still being investigated for germline mutation. Of the remaining 15 cases, 10 showed the presence of BRAF V600E mutation, two showed hypermethylation of the MLH1 promoter, and one showed germline MLH1 mutation. Two cases showed no BRAF V600E mutation, no MLH1 promoter hypermethylation or germline gene mutation. Overall, of 116 cases, three cases have confirmed Lynch syndrome with the detection of a germline mutation, two cases most likely have Lynch syndrome but without any detectable germline mutation of MLH1 or PMS2 using the current detecting methods. Conclusions: Our system-based screening algorithm using reflex immunohistochemistry of four MMR proteins has resulted in excellent detection rate of approximately 4% to 5% (5 out of 116 cases), consistent with the expected Lynch syndrome prevalence rate in the population. This represents a marked improvement over our previous family history-based approach in Lynch syndrome screening.