Urticaria pigmentosa localized on radiation field

A woman previously treated by radiotherapy for a breast cancer developed urticaria pigmentosa mainly restricted to the irradiation field, without any systemic symptoms. Localized forms of urticaria pigmentosa are exceptional, and their triggering factors are poorly understood. Several hypotheses can be discussed in this peculiar observation, among which a direct role of radiotherapy in the occurrence of cutaneous lesions cannot be ruled out.