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Racial difference in DNA mismatch repair deficiency associated with Lynch syndrome among colorectal cancer patients.

Krysta Contino, Robin Irons F, Kathryn Behling C, Tina Bocker Edmonston, Yize Wang R

Introduction: Lynch syndrome accounts for approximately 3% of all colorectal cancers (CRC) in the United States. African American (AA) patients are at a higher risk for CRC and diagnosed at a younger age and more advanced stage. The prevalence of LS among AAs has not been well studied. We hypothesized that AAs differ from non-Hispanic Whites (NHWs) in the prevalence of CRC secondary to DNA mismatch repair (MMR) deficiency.

Methods: We retrospectively studied 91 CRC patients screened for MMR deficiency between 03/2014 and 03/2016 at our institution. Immunohistochemistry staining was used to examine expression of MLH1, MSH2, MSH6 and PMS2. The Student’s t-test, chi-square test, and Fisher’s exact test were used in statistical analysis.

Results: Compared to NHW patients (n=68), AA patients (n=23) trended toward younger age (mean ± standard deviation [SD]: 54.0 ± 13.6 vs. 59.3 ± 10.7 years, p=0.06) and tumor location in the right colon (56.5 vs. 36.9%, p=0.10) and were similar in percentage of female patients, body mass index, and TNM stage. Among NHWs, 8 (11.7%) had loss of MLH1/PMS2, 1 (1.5%) had loss of MSH2/MSH6, and 1 (1.5%) had loss of PMS2 only. In contrast, all AAs had intact MMR protein expression. The difference in MMR deficiency between NHW (14.7%) and AA (0%) patients was statistically significant (p<0.05).

Conclusion: We found that the rate of MMR deficiency is lower in AA CRC patients compared to NHW patients. This finding warrants further study as it has significant implications for Lynch Syndrome screening in AA patients.