An Uncommon Case of Colonic Neuroendocrine Carcinoma with Scalp Metastasis

Introduction/Objective Neuroendocrine neoplasms of the colon account for <1% of all colorectal malignancies. While visceral metastasis of neuroendocrine neoplasms is commonly observed, cutaneous distant metastasis has infrequently been reported and correlates with an advance stage and progression of disease. To our knowledge, there have been only 10 cases of neuroendocrine neoplasms with metastasis to the scalp reported in the literature. Herein, we report an unusual case of colonic neuroendocrine carcinoma with scalp metastasis, that can be microscopically indistinguishable from the highly aggressive cutaneous neuroendocrine carcinoma, Merkel Cell Carcinoma. Methods/Case Report A 47-year-old female with a history of ileocecal neuroendocrine carcinoma and status post right hemicolectomy had developed liver metastasis and subsequently had an orthotopic liver transplant. PET scan later revealed multiple areas of increased activity involving the ribs, scalp and cervical lymph node that were concerning for malignancy. The scalp lesion consisted of a 7mm non-tender, mobile, violaceous, erythematous dermal nodule that was clinically concerning for cutaneous metastasis. A skin punch biopsy microscopically revealed a subcutaneous infiltrate of nests composed of neoplastic monotonous blue cells with the classic nuclear “salt and pepper” chromatin and scant eosinophilic cytoplasm. The lesional cells showed positive immunoreactivity for synaptophysin and chromogranin. With the given patient’s clinical history and presentation, the observed histological findings and immunophenotypic expression of the tumor cells supported a diagnosis of metastatic neuroendocrine carcinoma. Results (if a Case Study enter NA) N/A Conclusion Metastatic neuroendocrine carcinoma to the scalp is a rare entity and is infrequently encountered in dermatopathology. Given the location and the gross appearance of the scalp lesion, a wide differential diagnosis would include both benign and malignant tumors. In particular, Merkel Cell Carcinoma can grossly and histologically mimic metastatic colonic neuroendocrine carcinoma. Both entities would show synaptophysin and chromogranin uptake. However, metastatic tumors originating from the colon will demontrate CDX2 and SATB2 nuclear staining. We share this rare case of metastatic colonic neuroendocrine carcinoma as it is an important differential diagnosis for primary cutaneous Merkel Cell Carcinoma.