Abstract
RATIONALE: Collision tumors involving differentiated thyroid carcinomas are exceedingly rare, despite the overall high prevalence of thyroid cancer. PATIENT CONCERNS: A 65-year-old man was incidentally diagnosed with thyroid cancer during a staging workup for gastric cancer. DIAGNOSES: The histopathologic examination revealed 2 coincident cancers of the left thyroid lobe: papillary carcinoma (pT1bN1a) and follicular carcinoma (pT2N0). INTERVENTIONS: The patient underwent total thyroidectomy with central lymph node dissection, followed by thyroid hormone suppression and radioactive iodine therapy. OUTCOMES: No postoperative complications or cancer recurrence has been observed to date. LESSONS: This case highlights the diagnostic challenges and surgical considerations associated with collision tumors of the thyroid. Appropriate management remains controversial; therefore, further case studies and consensus guidelines are necessary.