Although extremely rare, thyroid collision tumors are typically medullary thyroid carcinoma (MTC) or papillary thyroid carcinoma (PTC), according to a new study published in Annals of Medicine and Surgery.

The researchers reviewed 8 cases and the available literature on this tumor type. The retrospective study found that partial or complete thyroidectomy was the treatment of choice for these patients and was associated with good survival.

“Collision tumors are extremely rare, with occasional case reports in the colon, lungs, ovaries, liver, stomach, and kidneys,” the authors explained. “However, despite thyroid neoplasia being the most reported endocrine malignancy (2.1%), patients with thyroid collision tumors have rarely been observed in the literature, with most thyroid collision tumors consisting of papillary and medullary carcinoma.”


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Only 33 cases of thyroid collision tumors were reported in the literature until 2015. Their etiology is unclear, but several theories have been proposed based on 1) a single pluripotent stem cell origin or 2) one tumor leading to an oncogenic microenvironment that stimulates the development of another tumor, or 3) a random meeting of two entirely different tumors.

The tumors occur more commonly in women and in middle age or later. Given the limited evidence and understanding of these tumors, their diagnosis and management are challenging. In this study, thyroid function tests and other laboratory findings were normal and ultrasound revealed nodular thyroid.

Four cases underwent total thyroidectomy and the other 4 underwent lobectomy. One case was lost to follow-up, but the rest had good outcomes. Given that almost 20% of cases of MTC are inherited syndromes, the authors strongly recommend prospective family screening for mutated RET genes for these patients.

Reference

Abdullah AM, Qaradakhy AJ, Ahmed MM, et al. Thyroid collision tumors; a case series with literature review. Ann Med Surg. 2022;76:103444. doi:10.1016/j.amsu.2022.103444