A case of tegafur/gimeracil/oteracil (TS-1)-induced acral hyperpigmentation: correlation between histopathological features and dermoscopic findings

Dermoscopy helps detect melanoma on the acral volar skin. A parallel ridge pattern is one of the characteristic dermoscopic findings of melanoma but is also seen in benign lesions, including drug-induced hyperpigmentation. Histological examination is therefore necessary for definitive diagnosis. A 74-year-old Japanese man was referred to our department with irregular-shaped brown macules on his palms and soles. The pigmented lesions had a parallel ridge pattern on dermoscopic examination. The largest lesion was resected at the patient’s insistence and considering the possibility of melanoma. Histopathological examination revealed increased melanin granules in basal keratinocytes and many melanophages in the superficial dermis, especially underlying the crista profunda intermedia, agreeing with the dermoscopic findings. The patient had been receiving tegafurgimeracil- oteracil (TS-1) for advanced gastric cancer. The pigmented lesions gradually regressed after cessation of TS-1, consistent with TS-1-induced hyperpigmentation. Further studies are needed to elucidate the pathogenesis, including analyses of the relationship between acrosyringeal endothelin-1 expression and the presence of volar melanocytes in relation to potential drug metabolism.