Abstract:

A 75-year-old woman with a remote history of medullary thyroid carcinoma (MTC), status post total thyroidectomy and radical neck dissection with positive lymph nodes forty-four years prior presented with a subcutaneous nodule of the left lower back of 5 years duration. The lesion was clinically diagnosed as an epidermal inclusion cyst in 2016, which coincided with a steady increase in serum calcitonin. Extensive evaluation failed to identify recurrent or metastatic MTC. Given symptoms of pruritis and growth of the nodule, the lesion was excised. Histopathology showed a well-circumscribed, dermal-based multinodular neoplasm composed of multiple nests of monomorphic epithelioid cells with admixed hyalinization and deposition of pink amorphous material. Cells stained positively for cytokeratin 7, thyroid transcription factor-1 (TTF-1), insulinoma-associated protein-1 (INSM1), and calcitonin. Congo red staining demonstrated apple-green birefringence under polarized light in the pink amorphous material, consistent with amyloid-rich stroma. Overall, the findings are consistent with metastatic MTC. Although cutaneous metastases from MTC are rare, their presence typically indicates widely disseminated disease and confers a poor prognosis. Clinically, they present as tender, pruritic, or ulcerated skin-colored or blue-colored nodules that typically appear on the chest or scalp. The TTF-1 positive staining may mimic metastatic lung carcinoma; however, positive calcitonin staining and amyloid deposition can be important clues to the diagnosis. Neuroendocrine differentiation, including staining for INSM1, chromogranin, and synaptophysin, may also be seen. In patients with the appropriate clinical history, it is important for dermatologists and dermatopathologists to consider cutaneous MTC while evaluating skin lesions, as this diagnosis can mimic benign entities.

Financial Disclosure:
No current or relevant financial relationships exist.

Menu

Noelle Lemons, MD