Flow cytometric immunophenotyping of serous effusions and peritoneal washings: comparison with immunocytochemistry and morphological findings

Aim-To evaluate immunophenotyping by means of flow cytometry as a complemen tary method for the detection of malignant cells in serous effusions and pe ritoneal washings. Material and methods-Frozen samples of 49 fresh serous effusions and perito neal washings were analysed by flow cytometry, using monoclonal antibodies against CD45, Ber-EP4, and N-cadherin. Results were compared with smear and cell block morphology, as well as immu nocytochemistry on paraffin wax embedded cell blocks. Results-Seventeen spe cimens were cytologically diagnosed as malignant, whereas 25 were interpret ed as benign. The remaining seven specimens were diagnosed as indeterminate or suspicious for malignancy. Ber-EP4 positive cells were detected in 16 o f the 17 cytologically malignant effusions, ars well as in five of seven su spicious cases and five of 25 specimens with benign cytology. In the latter group, three specimens showed atypical or malignant cell groups that were missed in routine morphological evaluation. In two additional samples, obta ined from patients with benign and borderline ovarian tumours, Ber-EP4 posi tive cells showed benign or mildly atypical features, and were interpreted as exfoliated benign or borderline malignant epithelial cells of tubal orig in, or as endosalpingiosis. All five Ber-EP4 positive indeterminate specime ns showed atypical or malignant cells on re-evaluation, and were Ber-EP4 po sitive in four of five cases using immunohistochemistry in cell block secti ons. Large numbers of CD45 positive and relatively few N-cadherin positive cells were detected in most specimens with the use of how cytometry, when c ompared with morphological evaluation. Conclusions-Flow cytometry is a rapid and highly effective method for the e valuation of effusions and peritoneal washings. The detection of Ber-EP4 po sitive cells using flow cytometry is strongly indicative of the presence of carcinoma cells in effusions and peritoneal washings. Although false posit ives are relatively infrequent, all specimens should be carefully evaluated morphologically to prevent the diagnosis of benign epithelial clusters as malignant.