Microsatellite instability among individuals of Hispanic origin with colorectal cancer

Although the presence of microsatellite instability (MSI) in patients with colorectal cancer (CRC) may have implications for prognosis, therapy, and family counseling, to the authors' knowledge, the prevalence of MSI has not been well described among individuals of Hispanic origin with CRC residing in the United States.

A retrospective cohort study using a hospital-based tumor registry to identify individuals of Hispanic origin who were diagnosed with CRC was conducted. Clinical data and tumor samples were retrieved. Molecular analyses included testing for MSI using a panel of 5 mononucleotide markers (BAT25, BAT26, NR21, NR24, and NR27) in a pentaplex polymerase chain reaction assay, as well as immunohistochemistry for the mismatch repair (MMR) proteins mutL homolog (MLH) 1, mutS homolog (MSH) 2, MSH6, and postmeiotic segregation increased 2 (PMS2) 2 on representative tissue.

A total of 111 individuals of Hispanic origin with CRC were identified. Approximately 41.4% were women, and the median age was 57 years (interquartile range [IQR], 47.1-63.5 years). Eleven patients (9.9%; 95% confidence interval [95% CI], 4.2%-15.6%) had MSI CRC, whereas 14 patients (12.6%; 95% CI, 7.3%-21.8%) had CRC with ≥1 MMR protein abnormality. Ten of 11 individuals with MSI had clinical or molecular characteristics suspicious for Lynch syndrome such as abnormal expression of MSH2 and/or MSH6 (n=7) or age<50 years at the time of diagnosis (n=7).

The prevalence of MSI CRC among Hispanic individuals may be similar to that of other races and ethnicities, but clinicopathological characteristics, including age at diagnosis and pattern of abnormal MMR protein expression, suggest that sporadic MSI CRC may be less common in individuals of Hispanic origin, and that much of the MSI observed in this situation may be attributable to Lynch syndrome. Further exploration of the causes of disparate presentations of CRC by ethnicity and race is warranted.