Cytokeratin immunohistochemistry: a procedure for exclusion of pregnancy in chorionic villi-negative specimen.

ABSTRACT

The confirmation or exclusion of the presence of products of conception (POC) in biological material may be crucial. This analysis has been undertaken to check how efficient the H&E examination of the putative POC specimen is in practice and to prove the hypothesis that the use of cytokeratin immunostaining can increase the diagnostic accuracy. Of 1078 POC specimens, 94 cases which were signed out as 'No chorionic villi identified' or 'Negative for POC' and in which all submitted material was histologically examined, were re-reviewed histologically and examined immunohistologically using the low molecular weight cytokeratin antibody CAM5.2. In six cases, the originally missed trophoblastic cells were found on re-review of the H&E slides, which was confirmed by CAM5.2 immunostaining. Of seven further cases which were suspicious for trophoblastic cells on re-review, three cases were positive for trophoblastic cells by CAM5.2 and four were negative. Of the remaining 81 cases negative for trophoblastic cells on H&E re-review, CAM5.2 was positive for the trophoblast in 13 (16 per cent). There were no false positive cases on CAM5.2 immunostaining of the endometrial curettings in 22 ectopic pregnancies and 22 cases with dysfunctional endometrial bleeding clinically and secretory endometrium histologically. Therefore, although the overall efficiency of the original diagnosis could have been as high as 98 per cent (1029 of 1051), the false negative rate was 23 per cent (22 of 94) in the chorionic villi-negative material. Even though the morphology of trophoblastic cells on conventional H&E staining is well known, it may be practically difficult to exclude pregnancy by the examination of uterine contents using conventional H&E staining only. The use of the cytokeratin immunostaining can decrease the rate significantly and should be considered in all chorionic villi-negative specimens without obvious extravillous trophoblasts.