Phenotypic Appraisal of Collision Tumors of Thyroid – Initial Experience of a Rare Entity at a Cancer Centre in South India

Introduction: Collision tumours (CT) of the thyroid refer to the coexistence of two or more independent, histologically distinct malignant tumours. Though the presence of multifocal differentiated thyroid carcinomas is common, it is extremely rare for the thyroid to harbour more than one type of malignancy simultaneously. Methods: An extensive literature search of PubMed databases identified very few cases indicating the tumour rarity. To the best of our knowledge, this is the first documentation of a case series including various combinations of CT in the thyroid. Our main aim is to explore the phenotypic characteristics of CT in the thyroid with an aim of revealing unique features associated with this rare entity. Results: Of a total of 138 thyroid cancers treated during the eight-year period, five (3.62%) were diagnosed as CT. All were females with a median age of 50 years. Papillary Thyroid Carcinoma (PTC) was the major component (80%) in collision with medullary (MC), follicular, and hurthle cell carcinomas. Both cases with papillary microcarcinoma showed vascular emboli and patients with a combination of MC and PTC had nodal metastasis. 80% of patients had a survival of more than 2.5 years and are alive without disease at present. Our study showed features like female predominance and PTC as the most common component with good overall survival. Metastatic and survival rates were consistent with matched singleton pathology. Conclusion: Insight into the genomic and proteomic pathways of this entity is the need of the hour.