Recommendations from the EGAPP Working Group: can UGT1A1 genotyping reduce morbidity and mortality in patients with metastatic colorectal cancer treated with irinotecan?

Of Recommendations: The Evaluation of Genomic Applications in Practice and Prevention (EGAPP) Working Group found that the evidence is currently insufficient to recommend for or against the routine use of UGT1A1 genotyping in patients with metastatic colorectal cancer who are to be treated with irinotecan, with the intent of modifying the dose as a way to avoid adverse drug reactions (severe neutropenia). Rationale: The EGAPP Working Group (EWG) found no intervention trials showing that targeted dosing of irinotecan based on UGT1A1 genotyping could reduce the rates of two specific adverse drug events, severe (Grade 3-4) neutropenia or diarrhea. Observational studies indicate a significant association between UGT1A1 genotypes, particularly *28/*28 and *1/*28, and the occurrence of severe neutropenia. Observational studies also indicate a possible association between severe diarrhea and these UGT1A1 genotypes, but the association is not statistically significant. An additional finding was the suggestion that reducing irinotecan dose may result in patient harms due to diminished effectiveness of treatment in highest risk individuals (*28/*28 homozygotes), and that a higher dose might be warranted among individuals at lower risk of adverse drug events (*1/*1 and *1/*28 genotypes). This review did not consider higher risk patients (e,g., having previous adverse reactions to irinotecan or additional risk factors for neutropenia). Analytic Validity: The EWG found adequate evidence to conclude that analytic sensitivity and specificity were high for the commonly tested alleles, but evidence was inadequate for rarer alleles. Clinical Validity: The EWG found adequate evidence of a significant association between UGT1A1 genotype and the incidence of severe neutropenia at standard doses of irinotecan. The EWG found adequate evidence of a possible association between genotype and severe diarrhea, but the effect was smaller and not statistically significant. The EWG found adequate evidence of a significantly higher rate of tumor response to standard irinotecan dosing among individuals with the genotype at highest risk of adverse drug events (*28/*28). Clinical Utility: The EWG found no evidence to support clinical utility in the proposed clinical scenario. Preliminary modeling Suggests that, even if targeted dosing were to be highly effective, it is not clear that benefits (reduced adverse drug events) outweigh harms (unresponsive tumors). Contextual Issues: Addressing patient preferences regarding risk of side effects and quality of life, versus aggressive treatment to potentially improve effectiveness, is expected practice. In addition, a recent study reported that risk for neutropenia was lower at lower irinotecan doses. For treatment regimens utilizing lower irinotecan doses, UGT1A1 genotype may not be a useful indicator of risk for adverse drug events. Further rigorous evaluation of UGT1A1 genotyping using current and promising irinotecan treatment protocols is warranted. Genet Med 2009:11(1):15-20.