Collision tumor of thyroid: A case report of synchronous papillary and follicular thyroid carcinoma.

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.