Supplementary Material for: Oestrogen receptor positive metastatic eccrine porocarcinoma: A case report and review of anti-oestrogen therapy in rare cancers.

Rare cancers, in aggregate, represent a significant burden of disease in oncology, and remain therapeutically challenging to manage due to a lack of clinical trials. Eccrine porocarcinoma is a rare cutaneous sweat gland malignancy for which there remains no standard approach to metastatic disease. We describe a patient diagnosed with metastatic disease, confirmed on bone biopsy; pathological analysis further revealed this was oestrogen receptor positive. She was commenced on the aromatase inhibitor letrozole and denosumab, and showed a significant clinical and radiological response on bone scan within 7 months. At the time of report, over 2-years since commencing letrozole, she remains well with no evidence of progression. Our experience adds to the literature suggesting anti-oestrogen therapy can have significant benefit in patients with ER positive non-breast cancer, and is in keeping with increasing interest in therapies agnostic to site of origin but guided by expression/mutation of oncogenic drivers.