Supplementary Material for: Metastatic ductal eccrine adenocarcinoma with excellent response to immunotherapy

Eccrine carcinoma, a subtype of which is ductal eccrine adenocarcinoma (DEA), is a rare cutaneous malignancy. For metastatic eccrine carcinoma there is very limited data to guide treatment. Conventional chemotherapy is of limited benefit and there is a only a small body of evidence for the use of immunotherapy in non-DEA eccrine carcinomas. We report the first case of metastatic DEA treated with a multimodality approach including surgery, radiotherapy and immunotherapy, with an excellent prolonged response to pembrolizumab, and provide a review of the literature on pathological and management aspects for this rare tumour subtype. A 60-year old male with a history of pT1N0M0 left scalp DEA, managed two years prior with excision and adjuvant radiotherapy, represented with a symptomatic right pontine metastasis. Imaging demonstrated intracranial, pulmonary and hilar disease; biopsy of the cranial and lung lesions showed metastatic adenocarcinoma, morphologically similar to the previously-resected scalp DEA. The patient was treated with stereotactic resections of his pontine metastases and adjuvant cranial radiotherapy, then commenced on immunotherapy with pembrolizumab. The patient has completed 21 months of pembrolizumab with a significant radiological response of the pulmonary and hilar disease and nil evidence of intracranial recurrence or further metastases. In this case report, we provide the first evidence of efficacy of immunotherapy in metastatic DEA, demonstrating an excellent and prolonged response of metastatic DEA to pembrolizumab. Further research is required to better establish the role of immunotherapy within the management protocol for this uncommon but aggressive tumour subtype.