Malignant melanoma arising in melanin-producing medullary thyroid carcinoma

HRAS-mutated primary thyroid malignant melanoma or medullary thyroid carcinoma with melanocytic dedifferentiation? A singular case with an ontogeny-phylogeny quandary

Melanotic pigment in the thyroid is practically synonymous with chronic minocycline therapy and rare cases of melanotic medullary thyroid carcinoma. However, primary melanoma of the thyroid has not been reported yet. We report a rare case of a 25-year-old male with a locally aggressive thyroid mass and distant metastases at presentation. Radiologically, a 8.3×7.6-cm nodule was identified in the right thyroid lobe. Fine-needle aspiration cytology (FNAC) showed discohesive atypical plasmacytoid cells with prominent nucleoli and no cytoplasmic pigmentation. Serum calcitonin levels were normal. A trucut biopsy showed a malignant tumor with a similar cytomorphology, including marked nuclear pleomorphism. In addition, intracytoplasmic melanin was seen in <1% of cells. Tumor cells were immunonegative for AE1/AE3, TTF1, synaptophysin, and chromogranin while positive for SOX10, S100P, HMB45, and Melan A, confirming the diagnosis of malignant melanoma, without any detectable MTC component in the biopsy. An HRAS G13R mutation was detected on NGS, which, intriguingly, is a known mutation in MTC, and exceedingly rare in melanocytic lesions. No other clinically or radiologically apparent primary lesion was identified elsewhere in the patient. The unusual histology and hitherto unreported molecular findings make this case of primary thyroid melanocytic neoplasm worth reporting. Abstruse origin of melanoma cells in the thyroid gland with molecular signature suggestive of MTC in our case raises a nomenclature and management conundrum, prompting us to revisit the "ontogeny recapitulates phylogeny" theory.

Melanin-producing medullary thyroid carcinoma with transformation to melanoma: A case report

Only one case of melanoma arising from melanin-producing medullary thyroid carcinoma (MTC) has been reported previously. In the present study, a second such case was reported and compared with the previous one. The patient was an 86-year-old male who presented with a right anterior neck mass. Ultrasound revealed a nodule measuring 49x48x40 mm in the right lobe of the thyroid. The levels of serum calcitonin (2,298 pg/ml) and carcinoembryonic antigen (CEA; 27.0 ng/ml) were markedly elevated. Aspiration cytology revealed suspected malignant anaplastic thyroid carcinoma and total thyroidectomy without neck nodal dissection was performed. On gross observation, the nodule was well encapsulated, soft, solid and black. Light microscopy indicated that the nodule was composed mainly of large, occasionally huge, pleomorphic cells with a solid or alveolar growth pattern. On immunohistochemistry, these cells were positive for melan-A and S-100 protein, and negative for thyroid transcription factor 1, calcitonin, chromogranin A and CEA. In the subcapsular area, melanin-producing MTC was intimately intermingled with the pleomorphic cells. No primary site of the melanoma was detectable in other organs. At three years after surgery, the patient died due to metastasis of the melanoma to the brain. The previously reported case had no detectable recurrence or distant metastasis up to 11 years after surgery. In comparison with that case, the present case had a similar morphology but the outcome was poorer. Thus, the prognosis of melanoma that transforms from MTC appears to remain uncertain.

Malignant carcinoma and skin melanoma neoplasms concomitantly in the thyroid

Malignant melanomas metastatic to the thyroid gland are uncommon. Based on microscopy and DNA methylation profile, we report a rare coexistence of neoplasms in the thyroid, presumably in our case, with relapse-free condition on adjuvant therapy.

Pathological characteristics and genetic features of melanin-producing medullary thyroid carcinoma

OBJECTIVE

To study the clinicopathological characteristics and genetic features of melanin-producing medullary thyroid carcinoma (MP-MTC).

METHODS

The immunophenotype of MP-MTC was studied using the immunohistochemical method, and its genetic features were assayed using an amplification refractory mutation system or PCR method.

RESULTS

A 71-year-old man presented with a slowly growing 5-cm mass on the left side of the neck for approximately two months. The cut surface of the neoplasm was brown and black. Melanin was found in the cytoplasm of tumor cells or the extracellular matrix. The tumor cells were positive for AE1/AE3, S-100 protein, melan A, HMB-45, synaptophysin, calcitonin, chromogranin A, melanoma, and thyroid transcription factor-1 (TTF-1) and negative for thyroglobulin. No typical genetic features were observed in this case. The patient showed no symptoms and recurrence at 12 months after the operation.

CONCLUSIONS

The tumor cells of MP-MTC were positive for melanin biomarkers, TTF-1 and exhibited no genetic features. Histopathology and immunohistochemistry of the tumor cells will aid accurate diagnosis.