Lichen planus arising in radiation therapy treatment sites.

A 59-year-old woman with a history of metastatic breast cancer presented for evaluation of hyperpigmented, reticulated, pruritic plaques on her left arm and left thigh after undergoing localized radiation therapy to the left breast and left thigh. These painful plaques with surrounding erythema appeared to follow Blaschko lines and punch biopsy results were histologically consistent with lichen planus. Herein we report a case of radiation-induced lichen planus.