Mixed neuroendocrine–non-neuroendocrine neoplasm (MiNEN) of the foreskin: a case report and literature review

Mixed neuroendocrine–non-neuroendocrine neoplasms (MiNENs) are rare composite malignancies defined by the coexistence of distinct neuroendocrine and non-neuroendocrine components within the same tumour. Although MiNENs are increasingly recognised in the gastrointestinal tract and less commonly in other sites, involvement of the penis or foreskin has not been previously reported. We describe what is up to our knowledge the first documented case of primary MiNEN of the foreskin in the literature. Our patient is a 71-year-old man, who presented with a foreskin mass, microscopically showed a high-grade neuroendocrine carcinoma component and a squamous cell carcinoma component arising in a background of HPV-associated penile intraepithelial neoplasia (PeIN). Comprehensive clinicoradiological assessment did not identify an alternative primary neuroendocrine carcinoma elsewhere. The patient subsequently underwent bilateral inguinal sentinel node biopsy, which demonstrated metastatic neuroendocrine carcinoma in the right inguinal lymph node. This case broadens the recognised anatomical spectrum of MiNENs and underscores the role of high-risk HPV in their pathogenesis at a previously unreported site.