Associations of HLA‐C*01:02 and HLA‐B*46:01 with regorafenib‐induced erythema multiforme in Japanese patients with metastatic colorectal cancer

Regorafenib improves the survival of patients with metastatic colorectal cancer (mCRC); however, it is also characterized by detrimental dermal side effects that may require treatment cessation or modified dosing. In our previous prospective pharmacokinetic, pharmacodynamic, and pharmacogenetic studies, 17.5% (7/40) of the patients with mCRC had grade 3 erythema multiforme (EM) that caused treatment discontinuation. Haplotypes in genes encoding human leukocyte antigen (HLA) are associated with EM following the administration of drugs, such as allopurinol. This study examined the association between HLA haplotypes and regorafenib‐induced EM. Regorafenib was administered orally at 160 mg/body once daily for weeks 1–3 of each 4‐week cycle. To determine the HLA haplotypes, we used the WAKFlow HLA Typing Kit HLA‐A, ‐B, or ‐C. The carrier frequency of HLA‐C*01:02 in patients with EM (6/7) was higher than that in tolerant controls (8/33; odds ratio [OR] = 18.8, 95% confidence interval [CI] = 1.95–180, p = 0.00437). HLA‐B*46:01 was also associated with EM (OR = 11.6, 95% CI = 1.47–92.1, p = 0.0299). These associations were no longer significant after Bonferroni correction for multiple testing. Therefore, regorafenib‐induced EM in Japanese patients appears to be associated with specific HLA haplotypes but further validation is needed.