Collision Tumors of the Thyroid

"Collision tumors, rare neoplasms underlying two distinct histological types of carcinomas (with different origins) separated by normal tissue, are described in many organs including the thyroid gland, but to a lesser extent. We aim to overview the current published data concerning collision tumors of the thyroid (CTT). This is a narrative review considering papers published on PubMed through a search starting from the terms “collision” and “thyroid”. Inclusion criteria are full-length articles, the English language, the timeline from inception to December 2022, and original studies with different levels of statistical evidence. We followed the main types of thyroid carcinomas: differentiated thyroid carcinoma of papillary and follicular type, anaplastic/ undifferentiated/poorly differentiated carcinoma, respectively medullary thyroid carcinoma. We identified 92 papers based on the mentioned key words criteria. We excluded 54 papers (reviews or non-thyroid CTT or other topics outside our purpose). We included in the final analysis 38 papers: 34 case reports (1 patient per paper), 2 case series (2 individuals per each article), one case series of 3 subjects, and a single study of retrospective type (including 21 subjects) – a total of 62 patients on published cases which represents the largest study on published cases to our knowledge (according to our methodology) "