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Mismatch repair-deficient colorectal tumors no more common among Latinos

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January 12, 2018

Latino patients with colorectal cancer had a 13% prevalence rate of mismatch repair-deficient tumors, a rate that appeared consistent with those of non-Hispanic white patients, according to study findings.

Latino patients are more likely to present with colorectal cancer at an earlier age, are 20% to 40% more likely to present with advanced disease, and have a 20% to 30% increased stage-specific mortality than their white counterparts.

However, the reasons for these disparities are not completely understood.

Between 10% and 15% of colorectal cancer tumors are associated with microsatellite instability. In addition, genomic instability is often caused by a loss of DNA mismatch repair activity.

Charité Ricker, MS, genetic counselor at University of Southern California Norris Comprehensive Cancer Center and clinical instructor of medicine at University of Southern California Keck School of Medicine, and colleagues sought to determine the prevalence of hereditary syndromes among 265 patients (51.7% men; mean age at diagnosis, 53.7 years) enrolled in the Hispanic Colorectal Cancer Study. The population-based study assessed Hispanic or Latino patients with colorectal cancer identified through the California Cancer Registry or local hospitals surrounding Los Angeles.

All patients completed a telephone-based or in-person interview about demographic information, as well as lifestyle exposures during the 2 years prior to colorectal cancer diagnosis. These data included family history of colorectal cancer and other cancers, other medical diagnoses, physical activity, body health, and weight and other risk factors for colorectal cancer.

Researchers also performed a systematic review of medical records for each patient.

Among all patients, 21.2% reported a first- or second-degree relative with colorectal cancer, 3.4% of whom met Amsterdam I/II criteria — meaning they had three relatives with colorectal cancer (Amsterdam I) or other Lynch-syndrome associated cancers (Amsterdam II), one of whom was a first-degree relative of another in two successive generations, and at least one of whom was diagnosed when aged younger than 50 years.

About 38% of patients met one criterion of Bethesda guidelines — “Bethesda 1,” indicated they were diagnosed when aged younger than 50 years; “Bethesda 2,” indicated they had an additional Lynch syndrome-associated cancer diagnosis; “Bethesda 4,” indicated they had at least one first-degree relative with a Lynch syndrome-associated tumor, one of which was diagnosed before age 50 years; and “Bethesda 5,” which indicated the patient had at least two first-degree or second-degree relatives with Lynch syndrome associated tumors. A lack of data on pathology reports prohibited analysis of Bethesda 3.

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A total 161 patients underwent immunohistochemistry or microsatellite instability testing, of whom 13% had mismatch repair-deficient tumors (n = 21).

Patients who were female (61.9%), aged younger at diagnosis (50.4 ± 12.4 years), had proximal location (61.9%), and had a first-degree (23.8%) or second-degree (9.5%) family member with colorectal cancer appeared more likely to have mismatch repair-deficient tumors.

Thirteen patients with mismatch repair-deficient tumors had a germline mismatch repair mutation: six had MLH1, four had MSH2, two had MHS6 and one had PMS2. Researchers identified two other patients with MLH1 mutations who did not undergo immunohistochemistry or microsatellite instability testing.

Six patients had polyposis phenotype and 5.7% of all patients had Lynch syndrome.

“Further research is needed to understand whether there is a lower percentage of tumors with high [microsatellite instability] in the Latino population,” the researchers wrote. – by Melinda Stevens

Disclosures: The authors report no relevant financial disclosures.