Collision tumors of the thyroid: Review of literature and report of a case of papillary–Follicular collision tumor

Vijy Paul Thomas, Rahul George

Thyroid Research and Practice 2018 15(2):60-64

It is a known fact that thyroid malignancies are the most common of endocrine malignancies. Furthermore, differentiated thyroid malignancies including the papillary and follicular types are the most common among these malignancies of the thyroid. However, it is extremely uncommon to get a combination of two primary malignancies within the same thyroid gland. These combinations can be classified into collision tumors, mixed tumors, and composite tumors. Whenever such tumors have been described, they have almost always been combinations of papillary carcinoma and medullary carcinoma. Recently, a couple of cases of combinations of papillary and follicular carcinomas are being reported. It is difficult to completely explain the occurrence of such tumor types together in the same gland. Various theories have been proposed to explain this simultaneous occurrence such as the stem cell theory, collision theory, and the hostage theory. It is now accepted that these tumors should be considered more aggressive and having a higher risk of recurrence as compared to either of the tumors occurring independently. Treatment should be patient specific and is directed by the more aggressive of the tumors; however, no standardized protocols for diagnosis or treatment have evolved due to lack of significant information on their behavior.

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