Atypical carcinoid metastasis to the skin

Carcinoid tumors are derived from neuroendocrine cells, and are most frequently found in the gastrointestinal tract and bronchopulmonary system. Cutaneous involvement of carcinoid tumors is relatively rare, with isolated case reports in the literature. We detail a patient with stage IV pulmonary atypical carcinoid tumor with skin metastasis. This case is unusual because the patient did not have any erythema or induration of the scalp, only a complaint of pain. On biopsy, the tumor cells had cytologic features of a carcinoid tumor, but were arranged as infiltrating cords, small aggregates and single units, rather than the organoid or trabecular pattern seen in the primary tumor. Further, along with neuroendocrine markers, the tumor cells had the staining pattern of cytokeratin 7+/cytokeratin 20-/thyroid transcription factor-1+, supporting a carcinoid tumor of lung origin. Thus, this case of skin metastasis from an atypical pulmonary carcinoid tumor illustrates a unique clinical and histologic presentation.