Researchers reported the case study of a woman with breast carcinoma who had radiotherapy-associated cutaneous mastocytosis in Extraordinary Case Report. 

A 64-year-old woman presented with multiple, red-brown macules located on her left breast and her adjacent central chest. These macules were smooth in texture and measured approximately 1 to 3 mm in diameter. The right breast was unaffected. 

Despite this diagnosis, she was asymptomatic. Eighteen months prior, she was diagnosed with T2N1 left breast carcinoma; it was discovered to be estrogen/progesterone receptor-negative and HER-2 positive. Her physicians prescribed her a cocktail of drugs consisting of decotexal, carboplatin, trastuzumab, and pertuzumab. In addition, she underwent lumpectomy, external beam radiation therapy, and adjuvant Herceptin therapy. This clinical approach managed to put her in remission, with skin lesions restricted to the irradiation field only. 

A skin punch biopsy with hematoxylin and eosin-stained sections revealed an elevated number of superficial dermal interstitial mast cells with degranulation. Scattered eosinophils were noted, but there was no evidence of cytological atypia. In addition, the research team carried out Giemsa stain and KIT immunostaining, which led to a diagnosis of cutaneous mastocytosis. 

Read more about systemic mastocytosis etiology 

Further results from her laboratory findings confirmed the results: initial serum tryptase levels were high at 24 µg/L; a repeat test was still high at 22.3 µg/L. Kit mutation D819V testing in the peripheral blood was negative. 

Although her working diagnosis remains cutaneous mastocytosis, she is not on any current therapeutics because she has not had cutaneous/systemic episodes to date. The patient is currently followed-up closely to monitor for possible systemic disease. 

“[Cutaneous mastocytosis] and [systemic mastocytosis] are not widely recognized and may be underdiagnosed in the setting of post-radiation for breast cancer,” the authors concluded. “Although rarely reported, it is important for clinicians and pathologists to be aware of this diagnosis for patients presenting with rashes after radiotherapy.” 


Murphy M, Valentini R, Shaughnessy E. Radiotherapy-associated cutaneous mastocytosis in a patient with breast carcinoma. Case report and review of the literatureAm J Dermatopathol. Published online May 1, 2023. doi:10.1097/DAD.0000000000002404