Genetic differences in humans cause clinical difficulties in opioid treatment. Previous studies indicate that a single nucleotide polymorphism in the catechol-O-methyltransferase (COMT) gene (rs4680; p.Val158Met) may present as a predictive biomarker for the response to morphine treatment. In our previous pilot exploratory study, patients with a G/G genotype were demonstrated to require a higher dose of morphine, compared with patients with A/A and A/G genotypes. In the present study, the aim was to replicate the findings in an independent cohort of opioid-treatment-naïve patients exhibiting various types of cancer. This prospective study was conducted from 2011 to 2012 at the Kindai University Faculty of Medicine. A total of 50 patients with opioid-treatment naïve and histologically confirmed malignant neoplasms who were scheduled to undergo opioid treatment were evaluated in the present study. Assessments were conducted pre-treatment (day 1), post-treatment (day 1), and one week after treatment (day 8). The required dose of morphine on day 1 was significantly higher for patients with the G/G genotype of COMT, compared with those with the A/A and A/G genotypes (P=0.013). The results of the present study provide additional evidence that the COMT genotype may be a predictive biomarker for the response to morphine treatment.
