A comparative study of flow cytometry and histopathologic findings in thyroid follicular carcinomas and adenomas.

As a possible diagnostic aid in the often difficult histopathologic distinction of thyroid follicular carcinomas from adenomas based on invasion most flow cytometry studies have indicated a higher aneuploidy incidence in carcinomas. However, these reports often are difficult to analyze mainly due to nonuniformity of pathologic diagnostic criteria. The present study compares the flow cytometry results of 65 follicular tumors with pathologic findings based on the World Health Organization's specific diagnostic and staging criteria. Aneuploidy was significantly higher in the 28 cancers than in the 27 hypercellular (fetal and embryonal) adenomas (57% v 22%; P = .02). There was a high percentage of aneuploidy (75%; nine of 12 cases) in the widely invasive follicular carcinomas, compared with 40% (six of 15 cases) in the minimally invasive carcinomas, 22% (six of 27 cases) in the hypercellular adenomas, and 10% (one of 10 cases) in the normofollicular or macrofollicular adenomas. However, aneuploidy was not significantly different between the most difficult differential histopathologic diagnoses of minimally invasive follicular carcinoma (40%; six of 15 cases) and hypercellular adenoma (22%; six of 27 cases) (P = .12). Other data included relatively high frequencies of aneuploidy in hypercellular adenomas (29%; six of 21 cases) and diploid status of carcinomas (36%; 12 of 33 cases). In summary, although the overall findings show a trend toward increasing aneuploidy from well-differentiated and hypercellular adenomas to minimally and widely invasive follicular carcinomas, the aneuploidy data are inconsistent and indicative of its nonspecificity and limited diagnostic usefulness.