Collision tumor of a papillary and follicular thyroid carcinoma: A second case report in Saudi Arabia and literature review

Introduction A collision tumor is a rare occurrence in which two distinct tumor types coexist within an organ while maintaining distinct borders. Case A 61-year-old female referred to our clinic for the evaluation of a thyroid mass. Ultrasound revealed a large, solid, isoechoic nodule in the right lobe measuring 4.5 × 3.1 cm (TI-RADS category 3). Fine-needle aspiration biopsy was suspicious for a follicular neoplasm, Hürthle cell (oncocytic) type, Bethesda system class IV. The patient underwent right lobectomy, and the final pathology report revealed minimally invasive follicular carcinoma. Completion thyroidectomy revealed papillary carcinoma of the left lobe. Conclusion Managing thyroid collision tumors is challenging due to the presence of two distinct tumors with different biological aggressiveness, treatment options, and prognoses. Addressing how these factors influence treatment planning can enhance understanding of patient management and outcomes.