Cutaneous mastocytosis extending beyond a radiotherapy site: a form of radiodermatitis or a neoplastic phenomenon?

Ionising radiation is often used as an adjuvant in the management of breast cancer. Acute and chronic skin changes are well recognised complications associated with its use. We demonstrate a rare clinical presentation of cutaneous mastocytosis that occurred at the site of radiotherapy and then extended beyond this boundary, and ask whether this can be treated as a localised side effect of radiotherapy or whether the potential for systemic mastocytosis needs to be excluded.