Collision tumor of medullary and papillary thyroid carcinoma with coexisting follicular adenoma: a unique triple pathology case report and review of literature

Background: The synchronous occurrence of papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC) within the same thyroid gland is extremely rare, and their occurrence with follicular adenoma has not been reported yet. Such coexistence poses significant diagnostic and therapeutic challenges due to their divergent embryological origins, histopathology, and treatment responses. To our knowledge, this is the first reported case of the follicular variant of papillary carcinoma and MTC occurring alongside follicular adenoma. Case presentation: A 60-year-old male presented with progressive neck swelling. Physical examination revealed firm nodules in both lobes of the thyroid. Laboratory evaluation showed normal thyroid function but markedly elevated calcitonin levels. Ultrasound demonstrated large bilateral nodules, and fine-needle aspiration cytology was suspicious for PTC. Total thyroidectomy was performed. Histopathological examination revealed a minimally invasive follicular variant of PTC (1.4 cm) and a medullary carcinoma (1.2 cm) in the left lobe, alongside a large follicular adenoma (6.5 cm) in the right lobe. Immunohistochemistry confirmed the dual pathology, with calcitonin and synaptophysin positivity in the MTC component and thyroglobulin positivity in the PTC component. Postoperative staging was mpT1bN0M0. CT and whole-body iodine scan performed postoperatively showed no nodal or distant metastasis. At follow-up, both calcitonin and thyroglobulin levels normalized, with no radiological evidence of recurrence. Discussion and conclusion: The occurrence of a collision tumor along with follicular adenoma of the thyroid has not been reported in the literature. This case underscores the importance of high clinical suspicion, especially in patients with elevated calcitonin and indeterminate cytology. Early recognition, complete surgical excision, and tailored adjuvant therapy can result in excellent long-term outcomes.