WT-1 assists in distinguishing ovarian from uterine serous carcinoma and in distinguishing between serous and endometrioid ovarian carcinoma.

It has been suggested that WT-1 is helpful in distinguishing a primary ovarian serous carcinoma (OSC) from a primary uterine serous carcinoma (USC). Since both neoplasms are often disseminated at diagnosis and since USC often spreads to the ovary and vice versa, it may be difficult to ascertain the primary site. This is important, since adjuvant therapies for OSC and USC may differ. WT-1 staining patterns also differ between OSC and ovarian endometrioid carcinoma and so it is possible that WT-1 may assist in the distinction of these two neoplasms, which is sometimes problematic, especially with poorly differentiated tumours. This study aims to document the value of WT-1 in these settings. Cases of ovarian borderline serous tumour, primary peritoneal serous carcinoma (PPSC) and uterine endometrioid carcinoma were also studied. Cases of OSC (n = 38), USC (n = 25) (in five of these cases there was also a component of endometrioid adenocarcinoma), ovarian endometrioid carcinoma (n = 13), uterine endometrioid carcinoma (n = 7), ovarian borderline serous tumour (n = 16) and PPSC (n = 6) were stained with WT-1. Cases were scored on a scale of 0-3, depending on the percentage of positive cells. The intensity of staining was scored as weak, moderate or strong. There was positive nuclear staining of 36 of 38 (94.7%) OSC with WT-1. In most OSC (68.4%), >50% of cells stained positively and staining was usually strong. Five of 25 (20%) USC were positive with only two cases exhibiting staining of >50% of cells. All primary ovarian and uterine endometrioid carcinomas were negative. All PPSC were positive, usually with diffuse strong immunoreactivity. Fourteen of 16 borderline serous tumours exhibited positivity with WT-1. WT-1 is useful in distinguishing OSC (characteristically diffuse strong nuclear positivity) from USC (characteristically negative). However, rarely OSC is negative and occasional cases of USC are positive. WT-1 may also be helpful in differentiating poorly differentiated OSC from poorly differentiated ovarian endometrioid carcinoma.