A Rare Occurence: Metastasis of Medullary Thyroid Carcinoma
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A 74-year-old man with no personal or family history of cancer or thyroid disease presented to an orthopedic surgeon with a painful nodule in the left buttock. The nodule was speculated to be an inflammatory soft tissue tumor, and the patient was prescribed anti-inflammatory drugs. However, the mass and symptoms did not improve. He was referred to another hospital because of slow progression in the mass size and pain over a period of 1 year.

Magnetic resonance imaging (MRI) revealed a mass in the left gluteus maximus muscle with T1-weighted image low intensity, T2-weighted image high intensity, and short-TI inversion recovery very high intensity. Enhancement was seen in the mass after administration of gadolinium. Needle biopsy was performed, and the pathological findings showed adenocarcinoma. The tumor cells were positive for thyroid transcription factor-1 (TTF-1) on immunohistological staining.

The tumor was resected with wide margin to control local pain and prevent local progression. The resected specimen measured 80 × 55 × 25 mm and weighed 74 g. The cut surface showed a white solid tumor within the skeletal muscle. The size of the tumor was 33 × 18 mm. Immunohistochemically, tumor cells were positive for cytokeratin (CK)-AE1/3, CK7, TTF-1, CEA, calcitonin, synaptophysin, and chromogranin A, but negative for CK20, Napsin A, Pax8, and p40. These findings indicated metastasis of Medullary Thyroid Carcinoma(MTC). Congo red staining was negative for amyloid deposition.

Points worth Discussion :-
1. It has been reported that clinical neck lymph node metastases are detected in at least 50% of patients with MTC and that distant metastases are present in 5% or 10–20% of cases of MTC by the time of primary diagnosis. Metastatic sites outside the neck are usually observed in the liver, lungs, or bones.
2. This is the first report of MTC metastatic to soft tissue, and emphasize should be given on the fact that distant metastasis to soft tissue in patients with MTC is extremely rare.
3. It is noteworthy that the primary tumor was not detected in the thyroid gland by several imaging examinations since the initial clinical presentation in this case.

Source: https://wjso.biomedcentral.com/articles/10.1186/s12957-017-1293-2
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