Medullary thyroid carcinoma combined with papillary thyroid carcinoma: case report and literature review.

We investigated the clinicopathologic features, immunophenotype, (differential) diagnosis, pathogenesis, treatment, and follow-up of medullary thyroid carcinoma (MTC) combined with papillary thyroid carcinoma (PTC). A retrospective analysis of the clinical and pathologic features and immunophenotype was conducted in a patient with MTC and PTC. Relevant literature was also reviewed. Results of thyroid fine needle aspiration indicated malignant tumor in the right lobe of the thyroid, suggesting PTC; further analysis by biopsy confirmed this diagnosis. The left lobe exhibited MTC. Tumor metastases were absent from the lymph nodes of the left central area (0/2), and no tumor was present in the thymic tissue. In the right lobe and isthmus, PTC was observed, with a maximum infiltration diameter of 0.8 cm, and tumor metastases were absent from lymph nodes of the right central area (0/3). Immunohistochemistry of the left lobe was positive for calcitonin, CK, TTF-1, CD56, CgA, and Congo red, but negative for CK19, thyroglobulin, galectin-3, MC, and CEA, with a Ki-67 proliferation index of 1%. The right lobe was positive for CK19, galectin-3, and MC, but negative for CD56. The V600E mutation was detected in BRAF. MTC combined with PTC is a rare thyroid tumor. This condition is diagnosed mainly based on morphology, immunophenotyping, and molecular detection. It must be distinguished from other malignancies, such as thyroid follicular tumors, undifferentiated carcinoma, poorly differentiated carcinoma, transparent stellate tumor, and mixed PTC/MTC. Surgery and post-operative drug administration currently constitute the preferred treatments.