Features of mixed medullary thyroid tumors: An NCDB analysis of clinicopathologic characteristics and survival

Mixed medullary-papillary thyroid carcinoma (MMPTC) and mixed medullary-follicular thyroid carcinoma (MMFTC) are rare variants with little known regarding behavior and prognosis.

Using the National Cancer Database (NCDB), demographics, clinicopathologic features, treatment, and overall survival (OS) from patients with MMPTC and MMFTC were compared to more prevalent subtypes.

There were 296,101 patients: 421 MMPTC (0.14%), 133 MMFTC (0.04%), 263,140 PTC (88.87%), 24,208 FTC (8.18%) and 8,199 MTC (2.77%). Compared to PTC, MMPTC and MMFTC patients were older (p < 0.001) with a higher Charlson-Deyo comorbidity index (p < 0.001). Mixed tumors exhibited lower rates of nodal disease but more distant metastases compared to PTC (p < 0.001). MMPTC demonstrated lower estimated 10-year OS than PTC and FTC (76.04%vs 89.04% and 81.95%,p < 0.001), yet higher than MTC (70.29%,p < 0.001). MMFTC had a worse OS compared to all groups (63.32%,p < 0.001).

Patients with MMFTC had significantly worse OS compared to DTC, portending a worse prognosis.