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The association of age at the onset of CRC and the prevalence of a <i>KRAS</i> G12C mutation is unclear. A retrospective, multicenter study evaluating metastatic CRC patients from January 2019 to July 2023, treated at the Oncoclinicas units and tested for tissue based <i>KRAS</i>/<i>NRAS</i> and <i>BRAF</i> mutations in a centralized genomics lab. A mismatch repair (MMR) status was retrieved from different labs and electronic medical records, as were patient demographics (age, gender) and tumor sidedness. The chi-square test was used to examine the association between clinical and molecular variables, with <i>p</i> value < 0.05 being statistically significant. A total of 858 cases were included. The median age was 63.7 years (range 22–95) and 17.4% were less than 50 years old at the diagnosis of metastatic CRC. Male patients represented 50.3% of the population. The sidedness distribution was as follows: left side 59.2%, right side 36.8% and not specified 4%. The prevalence of the <i>KRAS</i> mutation was 49.4% and the <i>NRAS</i> mutation was 3.9%. Among <i>KRAS</i> mutated tumors, the most common variants were G12V (27.6%) and G12D (23.5%), while <i>KRAS</i> G12C was less frequent (6.4%), which represented 3.1% of the overall population. The <i>BRAF</i> mutant cases were 7.3% and most commonly V600E. Only five (<1%) non-V600E mutations were detected. MSI-high or dMMR was present in 14 cases (1.6%). In the age-stratified analysis, left-sidedness (<i>p</i> < 0.001) and a KRAS G12C mutation (<i>p</i> = 0.046) were associated with a younger age (<50 years). In the sidedness-stratified analysis, a <i>BRAF</i> mutation (<i>p</i> = 0.001) and MSI-high/dMMR status (<i>p</i> = 0.009) were more common in right-sided tumors. Our data suggest that <i>KRAS</i> G12C mutations are more frequent in early-onset metastatic CRC. To the best of our knowledge, this is the largest cohort in the Latin American population with metastatic CRC reporting <i>RAS</i>, <i>BRAF</i> and MSI/MMR status.