Clinical implications of UGT1A1*28 genotype testing in colorectal cancer patients

Metastatic colorectal cancer is frequently treated with irinotecan, a topoisomerase-I inhibitor. The UGT1A1 gene encodes for an enzyme that metabolizes irinotecan, and its genetic variants were shown to be associated with increased drug toxicity. We evaluated clinical outcomes associated with the UGT1A1*28 variant.

The study included 329 colorectal cancer patients from the Israeli population-based Molecular Epidemiology of Colorectal Cancer study who were treated with a chemotherapy regimen that included irinotecan. Patients with metastases or disease recurrence were followed up for a median period of 2 years after occurrence of the event. Study end points were appearance of grade 3-4 hematological and gastroenterological toxicity, hospitalization due to toxic events (mostly neutropenia, fever, diarrhea, or vomiting), length of hospitalization, and overall survival. UGT1A1*28 was genotyped from peripheral blood DNA by fragment analysis and reported as number of TATA sequence repeats in the promoter of the gene.

The 7/7 variant of UGT1A1*28 was detected in 11.9% of the 329 participants. Grade 3-4 hematological toxicity was significantly higher in 7/7 carriers compared with 6/7 and 6/6 carriers (48.0%,10.2%, and 7.7% respectively; P < .001), as was the risk of toxicity-related hospitalization (45.8%, 25.3%, and 14.4% respectively; P = .001). Both short-term death within 2 months of treatment start (12.8%, 5.2%, and 2.9%, respectively) and median overall survival (1.6, 2.0, and 2.4 years, respectively; P = .01) were significantly worse in the 7/7 carriers. The age/stage-adjusted hazard ratio for patients with the 7/7 genotype compared with 6/6 was 1.7 (95% confidence interval, 1.1-2.3).

The UGT1A1*28 7/7 genotype is strongly associated with severe hematological toxicity and higher hospitalization rate and predicts lower survival of colorectal cancer in users of irinotecan.