MIB-1 immunohistometry of follicular adenoma and follicular carcinoma of the thyroid gland

OBJECTIVE: To analyze cellular proliferative activity, MIB-1 immunopositivi ty of normal tissue (n = 20), follicular adenoma (n=30) and follicular carc inoma (n = 32) of the thyroid gland was analyzed by means of immunohistomet ry. STUDY DESIGN: Immunohistochemical reactions were performed on 3-mu m sectio ns from routinely formalin fixed and paraffin embedded surgical specimens u sing an indirect peroxidase method. The rate of immunostained cells was det ermined using the CM-2 TV image analysis system (Hund, Wetzlar, Federal Rep ublic of Germany). Forty viewing fields (1.94 mm(2)) were measured with 20: 1 objective magnification. An average of 5,965 cells were assessed in each case. RESULTS: Mean MIB-1 immunopositivity was higher in follicular carcinoma (av erage, 2.30%) and follicular adenoma (0.58%) than in normal thyroid tissue (0.14%). The distribution of single values differed significantly be tween groups (P <.001). To test the suitability of MIB-1 immunohistometry for the differential diagnosis of follicular adenoma and follicular carcinoma, dif ferent four-field tables with varying thresholds were calculated. Using a t hreshold of 0.9%,follicular carcinoma could be detected with a sensitivity of 75% (24/32) and a specificity of 83% (25/30). If a specificity of 90% is required (27/30), the sensitivity of the test decreases to 69% (22/32), ba sed on a threshold of 1.1%. CONCLUSION: As some overlap of single values has to be considered MIB-1 imm unohistometry, although presenting new insights into the proliferative pote ntial of thyroid lesions, is of only limited value for the differential dia gnosis of follicular lesions in routine surgical pathology.