Cellular cohesiveness in benign and malignant thyroid follicular tumours varies significantly, but the difference is not useful in diagnosis of individual cases

Abstract

The aim of our study was to search for new, readily available and statistically reliable cytological markers for differentiating benign and malignant follicular thyroid neoplasms pre-operatively. Cohesiveness of tumour cells in cytology slides from a series of 58 follicular tumours diagnosed between 1998 and 2004 inclusive was studied, including 48 follicular adenomas, and eight minimally invasive and two widely invasive follicular carcinomas. Photomicrographs of the cytology slides were taken and the digital images were analysed using computer image analysis software. We evaluated the relative proportions of cells arranged in groups of various sizes. The cohesiveness of the cells in cytological smears was then correlated with the immunohistochemical expression of E-cadherin in corresponding histological slides. Cases from 15 men (26%) and 43 women (74%) with a mean age of 50 years (range, 19-79) were analysed. In follicular adenomas and carcinomas, respectively, isolated cells were seen in 16.8% and 24.7% (P = 0.028), groups of two to five cells in 9.7% and 11.5% (P = 0.145) and groups of more than five cells in 73.5% and 63.8% (P = 0.041). The mean cell count in groups with more than five cells was 46.5 and 27.0 in adenomas and carcinomas, respectively (P < 0.001). Cell cohesiveness, either as percentage of cells in groups of more than five (R(2) = 0.026) or as mean cell count per group of more than five (R(2) = 0.005), was not found to be dependent on the expression of E-cadherin. Using a threshold of 13% isolated tumour cells in cytological smears, follicular adenomas and carcinomas could be distinguished with 90% sensitivity and 41% specificity. Although we demonstrated a statistically significant difference in cell cohesion between follicular adenomas and carcinomas, these could not be distinguished in the clinical setting by evaluation of the percentage of isolated cells in cytological smears because the specificity was too low. The absence of correlation of cellular cohesiveness with E-cadherin expression indicates that other factors are probably responsible for the loss of cohesiveness observed in follicular thyroid malignancy.