Abstract

Mixed neuroendocrine and non-neuroendocrine neoplasms (MiNENs) are uncommon in the head and neck and due to a lack of unified nomenclature and defining criteria, these tumors have remained under-recognized and poorly understood. In the rare instances when they do occur in this region, involvement of the larynx in elderly males is most frequently reported. In the gastrointestinal tract where they are well characterized, MiNENs usually have aggressive behavior and a dismal prognosis, driven by a high-grade neuroendocrine component. Due to the rarity of this diagnosis in the head and neck region and the use of inconsistent terminology, the prognosis and best therapeutic management of patients with MiNEN remains unknown. We report a case of primary cutaneous MiNEN occurring on the scalp of a 77-year-old male with an initial diagnosis of high grade carcinoma on shave biopsy. Clinically, the lesion was an ulcerated, raised nodule that measured 1.3 cm in greatest dimension. Wide surgical excision removed a 45 cm2 temporal scalp mass. Histologic examination and mutually exclusive immunohistochemical profiles confirmed the presence of two distinctive malignancies forming the ulcerated tumor: squamous cell carcinoma and Merkel cell carcinoma. The Merkel cell carcinoma was positive for INSM1, CAM5.2, CK20, and negative for TTF1. The squamous cell carcinoma expressed p40, CAM5.2, and TTF1 and was negative for INSM1 and CK20. Both malignancies were negative for Merkel cell polyomavirus. The absence of epidermal involvement argued against a collision tumor involving a coexisting invasive squamous cell carcinoma and the diagnosis of MiNEN was made. We report this case for its exceptional rarity and to discuss the current gaps in classification systems that may cause inaccurate categorization of these rare tumors.

Financial Disclosure:
No current or relevant financial relationships exist.