Small cell medullary thyroid carcinoma: A diagnostic dilemma

Area of Science:

• Endocrinology
• Oncology
• Pathology

Background:

• Small cell variant of medullary thyroid carcinoma (SCMTC) is a rare entity.
• Historically misdiagnosed as primary thyroid lymphoma before immunohistochemistry.
• Immunohistochemistry has clarified the rarity of SCMTC.

Observation:

• A patient presented with a year-long neck mass and a neoplastic lesion diagnosis.
• Serum calcitonin levels were normal, but serum carcinoembryonic antigen (CEA) levels were elevated.
• Diagnosis of SCMTC was confirmed post-thyroidectomy via immunohistochemistry (positive for AE1/AE3 and CEA, negative for calcitonin).

Findings:

• SCMTC is confirmed as a rare and aggressive subtype of medullary thyroid carcinoma.
• Elevated serum CEA levels can be a key diagnostic indicator in cases with normal calcitonin.
• The patient developed metastasis three months after radiotherapy.

Implications:

• Early and accurate identification of SCMTC is crucial due to its aggressive nature and poor prognosis.
• Serum CEA levels are valuable diagnostic markers when calcitonin is not elevated.
• Aggressive treatment strategies are warranted for SCMTC.