A very rare histological subtype of medullary thyroid carcinoma (MTC), known as spindle cell variant, was described in 4 cases.

“We reviewed 99 cases of MTC confirmed in our hospital from 2012 to 2019, only 4 cases spindle cell variant MTC meet the criteria, accounting for 4% of all MTC,” the authors said in a study published in Diagnostic Pathology.

The 4 patients (age range, 26-54 years, 50% male) described had visited the hospital due to the accidental finding of painless neck masses that enlarged gradually. The masses were diffuse, firm, and moved with deglutition. Family history did not reveal any relevant issue and the level of serum parathormone was normal.

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Ultrasound examination showed the presence of solid and hypoechoic nodules (2-6 cm in diameter) in the left (n=2) or right (n=2) lobe of the thyroid. They had clear boundaries, solid shapes, soft textures, and grayish-white or grayish-brown coloration. One case was gravelly calcified and another one had ipsilateral lymph node metastasis.

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The tumors had spindle cell morphology with cells arranged in fascicles or interweaves separated by fibrovascular or amyloid stromata. Moreover, tumor cells had abundant cytoplasm and short or long spindle nuclei, with inconspicuous nucleoli and rare mitoses.

Immunohistochemical staining showed positive expression of thyroid transcription factor-1, calcitonin, chromogranin A, synaptophysin, and CD56 in all 4 cases. The Ki-67 proliferative index was 3%-10%.

Patients were treated with total thyroidectomies with regional lymph node dissections (n=3) or thyroid mass resections (n=1). All patients were alive at follow-up (7-84 months after surgery).

At the time of the authors’ publication, there were only 5 cases of the spindle cell variant of MTC reported in the literature. “It is easy to mistake for other lesions due to its rarity and spindle cell morphology,” they said.


Wang YX, Yang SJ. Spindle cell variant of medullary thyroid carcinoma: a clinicopathologic study of four cases. Diagn Pathol. 2021;16(1):112. doi:10.1186/s13000-021-01152-w