Researchers showed the most common form of collision tumors in the thyroid included medullary thyroid carcinoma (MTC) and papillary thyroid carcinoma (PTC), as published in Archive of Clinical Cases.

PTC can often be found in the background thyroid of patients receiving surgery for MTC, and incidental findings from autopsies report as high as 35% of patients with MTC may also have PTC. A large case series of 196 patients with MTC found that 13.8% had concurrent PTC.

Studies also indicate that collisions of MTC and PTC occur twice as often in females than in males and are often discovered in the fifth, sixth, or seventh decade of life.

Continue Reading

These various hypotheses for the causes of collision tumors have been proposed over the years: 1 tumor forms first and creates an environment that facilitates the development of a second form, 2 cancers have a common cancerous stem cell lineage which differentiated into 2 separate cell lines, and that collisions are just the random coincidental result of 2 separate and distinct tumor types.

Read more about MTC epidemiology

Collisions between MTC and PTC may be the result of germline point mutations in the rearranged during transfection proto-oncogene causing tyrosine kinase activation. Some evidence has suggested that mutations of the rat sarcoma oncogene might be involved in the pathogenesis of some forms of collision tumors such as those between PTC and follicular thyroid carcinoma.

“Ultimately, a combination of theories should be considered, such as in the case of a coincidental metastasis in which seeding’s in the thyroid gland is favored by microenvironmental alterations,” the authors suggested. The combination of 2 distinct tumor types can also make clinical management difficult.

“Management of thyroid collision tumors is challenging, as collision tumors usually contain components with different aggressiveness, treatments options, and prognosis,” they said. “These tumors ought to be managed in a multidisciplinary framework and need to be individualized, considering biological aggressiveness and the stage of the tumor.”

Collision tumors are defined as when 2 histologically distinct neoplasms occur in the same organ and are separated by normal tissue without admixture. Collision tumors are also different from mixed tumors and composite tumors which are a result of a common driver mutation that causes different cellular populations in the same tumor.


Bojoga A, Stănescu L, Badiu C. Collision tumors of the thyroid. a special clinical and pathological entity. Arch Clin Cases. 2021;8(4):84-90. doi:10.22551/2021.33.0804.10191