The aim of this study was to evaluate the clinical utility of immunohistochemical staining of human testicular germ cell tumours with the monoclonal antibody 43-9F to distinguish embryonal carcinoma (EC) from other malignant germ cell components in order to facilitate pathohistological assessment of prognostic risk factors for metastatic disease in clinical stage I NSGCT. Archival, formalin-fixed, paraffin-embedded tissue blocks of 24 classical seminomas, 7 spermatocytic seminomas, and 20 non-seminomatous germ cell tumours were stained for 43-9F, AFP, hCG and PLAP expression. Immunohistochemical expression was graded using a semi-quantitative scoring system: 1+ = 0-25%, 2+ = 26-50%, 3+ = 51-75% and 4+ = 76-100%.
Positive immunohistochemical staining for 43-9F was found in all embryonal carcinomas and yolk sac tumours (YST); staining intensity was not statistically different between the two tumours (3.8 ± 1.2 vs. 3.1 ± 0.9). Classical seminomas and seminomatous components of NSGCT stained positive in 13/24 cases (54%); staining intensity was weak to moderate (1.1 ± 0.7) in all but two cases (4+). Spermatocytic seminomas demonstrated weak positive immunostaining in 2/7 cases (29%). Adjacent CIS was found in 33/54 (61.1%) of tumours and 24/33 (72.7%) of CIS cells exhibited a weak to moderate staining intensity (1.4 ± 0.7). AFP expression was found in 93% of YST and in only 10% of EC; however, based on the focal staining pattern, adequate differentiation of YST and EC was not possible. Positive PLAP staining was observed in 75% of EC, 79% of seminomas and in 88% of CIS cells. We did not find 43-9F staining clinically useful to distinguish embryonal carcinoma from other germ cell tumour components such as yolk sac tumour. The detection rate of CIS by 43-9F immunohistochemical staining was low and combination of PLAP staining with light microscopy was even superior. Additionally, our study confirms the link between pre-invasive CIS and embryonal carcinoma and suggests the possible direct development of embryonal carcinoma from CIS.