Background: Microsatellite instability (MSI) is present in up to 15% of sporadic colorectal cancers (CRCs) and explains the heritable etiology underlying CRC in Lynch Syndrome (LS). MSI occurs as a result of deficient mismatch repair (MMR) function, which influences CRC phenotype and predicts response to treatment. Data demonstrate a higher rate of MSI in Blacks than Whites; studies in Hispanics have demonstrated that MSI generally occurs in the context of LS. The prevalence and influence of these markers in the disenfranchised racial and ethnic populations of Florida are not described.

Objective: The present study describes the prevalence of MMR deficiency and MSI-high CRCs among racial and ethnic minorities in Miami-Dade County and examines the influence of MSI on CRC outcomes.

Methods: The Network Cancer Program database and Oncology Clinic records of the county safety net hospital and university-affiliated tertiary care referral center were queried to identify consecutive retrospective cases of CRC for the years 2005-2010. The pathology records confirmed availability of surgically resected tissue. The diagnosis of CRC was confirmed by chart review. Immunohistochemistry (IHC) for four MMR proteins (MLH1, MSH2, MSH6, and PMS2) was performed. In a subset of FFPE tumors, MSI testing was also performed by PCR. The prevalence of MMR and MSI abnormalities was determined among racial/ethnic groups. Results were evaluated for concordance and correlated with CRC endpoints.

Summary of Results: 249 CRCs were identified (non-Hispanic whites [NHW] 77, Hispanic 101, Black 71) with the following AJCC Staging: 0=4, 1=40, 2=74, 3=85, and 4=46. MMR deficiency was found in 11.6%; loss of MLH1/PMS2 was seen in 75.9% and MSH2/MSH6 17.2%. MMR deficiency rates by racial/ethnic group were as follows: NHW 10.4%, Hispanic 12.9%, and Black 9.9%. MSI was tested in 50 CRCs; microsatellite stability (MSS) was found in 84% and high levels of MSI in 16%. Excellent concordance was observed between MMR and MSI (Kappa=0.88).

Conclusions: MSI occurs frequently in our disenfranchised, largely immigrant patient population, supporting the utility of universal CRC screening among the underserved. MMR deficiency varies by racial and ethnic classification. The proportion of these MSI CRCs due to Lynch Syndrome needs to be clarified. MMR and MSI have excellent concordance as competing screening tests, making the cheaper MMR preferable, particularly for the underserved. The influence of race/ethnicity on other CRC endpoints is underway.

Citation Format: Daniel A. Sussman, Shivali Berera, Peter Hosein, Feng Miao, Tulay Koru-Sengul, Jacob McCauley, Erin Kobetz-Kerman, Olveen Carrasquillo, Maria T. Abreu. Microsatellite instability among disenfranchised minority colorectal cancer patients. [abstract]. In: Proceedings of the Sixth AACR Conference: The Science of Cancer Health Disparities; Dec 6–9, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2014;23(11 Suppl):Abstract nr B45. doi:10.1158/1538-7755.DISP13-B45

©2014 American Association for Cancer Research.
2014