Solid variant of papillary thyroid carcinoma - Incidence, clinical-pathologic characteristics, molecular analysis, and biologic behavior

Solid variant is a rare and poorly characterized variant of papillary thyro id carcinoma. In this study we analyzed 20 primary cases of the solid varia nt of papillary carcinoma found in a series of 756 papillary carcinomas ope rated at the Mayo Clinic between 1962 and 1989. The criteria for classifica tion-included predominantly (> 70%.) solid growth pattern of primary tumor, retention of cytologic features typical of papillary carcinoma, and absenc e of tumor necrosis. For each case of the solid variant, a control case of classical papillary carcinoma matched by age, sex, tumor size, and length o f follow-up was selected. The follow-up ranged from 6 to 32 years. Two pati ents with the solid variant of papillary carcinoma (10%) died from disease 7 and 10 years after initial surgery, while another two patients (10%) are alive with lung metastases. In contrast, the control Group had no cases wit h distant metastases or death from disease. Molecular analyses showed a sim ilar prevalence of RET/PTC rearrangements in both groups. In conclusion, th e solid variant of papillary carcinoma is associated with a slightly higher frequency of distant metastases and less favorable prognosis than classica l papillary carcinoma. However, it should be distinguished from poorly diff erentiated thyroid carcinoma, which has a reported lower survival rate comp ared with the solid variant of papillary carcinoma.