Incidence of Micropapillary Carcinoma in Total Thyroidectomy

Abstract

Objective (1) Compare prognostic factors in thyroid micropapillary carcinoma (MPC) <5 mm versus >=5 mm. (2) To compare MPC characteristics in patients with pre-existing thyroid carcinoma to patients with no other thyroid carcinoma. Methods Pathology results were reviewed for consecutive total thyroidectomy patients between 2002 and 2007 (n=835). Hemithyroidectomies and completion thyroidectomies were excluded. Statistical significance of the difference in incidences was calculated using Fisher's exact test and chi-squared analysis. Results MPC was found in 50.2% of total cases. Where the size was <5mm (64%), 9.3% extended beyond the thyroid capsule, 51.7% were multifocal, and 27.5% were bilateral. In MPCs >=5 mm (36%), the data showed 25.2%, 70.9%, 51%, respectively (p-value always < 0.05). In the 314 patients with no other thyroid malignancy, MPC was found in 47.1% of cases. 14.9% had capsular extension; 50% were multifocal, of which 56.8% were bilateral. In the 521 patients with malignant disease, the data showed 52.1%, 15.1%, 63.2%, and 63.3%, respectively, with p-values via Fisher's exact test .22, .112, .003, and .07. Conclusions In this study, MPC was found in 50.2% of patients. MPCs >=5 mm carried an increased risk for extracapsular spread, multifocality, and bilaterality. While patients with malignancies of the thyroid (aside from MPC) more commonly have multifocal MPCs, there was no significant difference in bilaterality, size, or extracapsular spread in MPCs in the presence of malignant vs. benign disease.