Lynch syndrome among gynecologic oncology patients meeting Bethesda guidelines for screening

Abstract

Objective: Lynch syndrome (LS) is characterized by a high lifetime incidence of colorectal cancer and gynecologic malignancies such as endometrial and ovarian cancer. Identification of LS families is important as it allows for heightened cancer screening which decreases colorectal cancer mortality. The original 1996 Bethesda guidelines included two gynecologic populations that should be further evaluated for LS: those with endometrial cancer before the age of 45 years and those with two LS-related cancers (i.e. synchronous endometrial and ovarian cancer). Our study aims to estimate the prevalence of LS in these two populations.

Methods: We utilized a diagnostic algorithm that included immunohistochemistry for mismatch repair protein expression followed by selective evaluation for microsatellite instability and MLH1 gene promoter methylation.

Results: Among 72 eligible patients, 9 (12%) had molecular findings consistent with LS: 6/50 (12%) in the early-onset endometrial cancer group and 3/22 (14%) in the synchronous primary cancer group. In an additional 3 cases, MLH1 silencing was due to promoter methylation: 1/50 (2%) in the early-onset endometrial cancer group and 2/22 (9%) in the synchronous primary cancer group. Of the 9 women with molecular criteria suggesting LS, only three had pedigrees meeting the Amsterdam criteria.

Conclusions: A diagnostic algorithm can identify patients with LS and those who warrant further genetic testing. Our findings reinforce the recommendation that women diagnosed with endometrial cancer before the age of 45 years and women with synchronous endometrial and ovarian cancer be screened for LS, irrespective of family history.

Figure 1

A. Immunohistochemistry results for MLH1, MSH2, and MSH6 The top row demonstrates normal nuclear staining for each mismatch repair protein. The bottom row demonstrates absent staining which is consistent with abnormal mismatch repair protein function. B. Representative example of microsatellite instability in endometrial cancer DNA (bottom) compared to matched normal DNA (top) in one of the NCI-recommended microsatellite markers. In this case, there is a shift in the peaks, representing an error in the DNA replication process and contraction of this microsatellite region. C. Methylation specific PCR results. Lane 1 contains the methylated control. For each case, two PCR reactions were performed with primers specific for the methylated MLH1 promoter (loaded on the left) and with primers specific for the unmethylated MLH1 promoter (loaded on the right). Cases 1 and 2 demonstrate tumors with MLH1 silencing due to MLH1 gene promoter methylation, while case 3 represents and case that may be due to an inherited germline MLH1 gene mutation.

Figure 2

Diagnostic algorithm used in our study. Dark blue boxes represent molecular findings consistent with Lynch Syndrome. Light blue boxes represent abnormal molecular findings that warrant further genetic testing for Lynch Syndrome.