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A case of Primary Testicular Plasmocytoma (PTP) in an 81-year-old man with a painless nodule in the left testis is reported. All possible pre-operative investigations were carried out, but the diagnosis of PTP was possible only after microscopic examination of the resected testis.

Background Merkel cell carcinoma is a rare and aggressive neuroendocrine tumor that commonly arises in the skin. It is rare for it to occur in the testes. There are only seven cases of testicular Merkel cell carcinoma reported in the literature. Case presentation A 66-year-old Maori man presented to our hospital with left testicular swelling. His alpha-fetoprotein and beta-human chorionic gonadotrophin levels were within normal limits. His lactate dehydrogenase concentration was elevated to 267 U/L. Ultrasound imaging confirmed a large testicular mass, and he underwent left orchiectomy. His histological examination revealed a neuroendocrine tumor with an immunostaining pattern suggesting Merkel cell carcinoma. He presented to our hospital again 3 months later with right testicular swelling that was confirmed on ultrasound sonography to be a tumor. He underwent a right orchiectomy, and his histological examination revealed metastatic Merkel cell carcinoma. A primary lesion was not identified, and computed tomographic imaging did not reveal spread to other organs. He received six cycles of adjuvant carboplatin and etoposide chemotherapy and remained disease-free 18 months after completion of chemotherapy. Conclusions Given the paucity of studies, standard adjuvant treatment for testicular Merkel cell carcinoma remains uncertain, although platinum-based chemotherapy seems to be an appropriate option. Electronic supplementary material The online version of this article (doi:10.1186/s13256-016-1102-5) contains supplementary material, which is available to authorized users.