A rare case of co-occurring medullary thyroid carcinoma (MTC) and papillary thyroid carcinoma (PTC) is described in a study published in the Open Journal of Pathology. MTC and PTC have different tissue origins and clinicopathological manifestations and rarely occur in the same patients, the authors wrote.

The 44-year-old female patient had MTC on the left side and papillary microcarcinoma subtype of PTC on the right side of the thyroid with no metastatic carcinoma in the central lymph nodes of both sides. Total thyroidectomy along with bilateral central lymph node dissection was performed. The patient had a favorable recovery with no complications and had no abnormalities at her 11-month follow-up.

“The origin, clinicopathological manifestations, and immunophenotypes of medullary thyroid carcinoma and papillary thyroid carcinoma are different. It is relatively rare for the two to occur at the same time,” the authors said. “The diagnosis mainly depends on the microscopic morphology and immunophenotype characteristics.”


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MTC generally originates from thyroid C cells and accounts for 1%-2% of thyroid cancers, while PTC derives from thyroid follicular epithelium and is the most common form of thyroid cancer, accounting for 85%-90% of cases.

Read more about MTC pathophysiology.

In general, 3 opinions on how co-occurring thyroid cancers might occur exist in the literature. The first involves the cancers originating from a common stem cell before they differentiated. A previous case study on another individual with both PTC and MTC found that the 2 cancers did not have a common stem cell ancestor.

A second theory is that both cancers have the same proto-oncogene such as RET. While some instances of both types of cancers have mutations in the RET proto-oncogene, the penetrance and activation mechanisms appear to be different between them. More research needs to be performed to determine whether abnormal RET gene expression may be involved.

The third opinion is the collision theory—that the 2 cancers are independent and occur together only coincidentally. The patient in this study fit more into this theory since the 2 cancers appear to have developed independently on opposite sides of the thyroid.

Reference

Liu S, Zhao Y, Zhao X. A case of medullary thyroid carcinoma combined with papillary microcarcinoma and literature review. Open J Pathol. 2022;12(03):71-79. doi:10.4236/ojpathology.2022.123009