OVX1 radioimmunoassay complements CA-125 for predicting the presence of residual ovarian carcinoma at second-look surgical surveillance procedures

At second-look surgical surveillance procedures, normal CA-125 levels can be associated with persistent disease in 50% to 60% of patients. A novel radioimmunoassay (RIA) has been evaluated for the ability to identify patients with persistent disease who have normal levels of CA-125. The OVX1 double-determinant assay used a murine monoclonal antibody to detect an epitope on a high-molecular weight mucin-like glycoprotein. Apparently healthy individuals had serum OVX1 levels of 2.23 +/- 2.48 U/mL (mean +/- SD). Elevated serum OVX1 levels (> 7.2 U/mL) were found in 5% of 184 normal individuals and in 70% of 93 epithelial ovarian cancer patients with clinically evident disease. Among sera from these ovarian cancer patients, OVX1 was elevated in 68% of 76 samples with CA-125 levels more than 35 U/mL and in 76% of 17 samples with CA-125 levels less than 35 U/mL. In serum samples obtained at the time of positive second-look laparotomy, 59% of 41 patients with CA-125 levels less than 35 U/mL had elevated OVX1 antigen levels, whereas 41% of 22 patients with CA-125 levels more than 35 U/mL had elevated serum OVX1 levels. In patients with negative second-look laparotomies, false-positive results were eliminated by increasing the threshold of OVX1 to 10.5 U/mL. At this level, 32% of 41 patients with positive second-look operations had an elevated OVX1 level, despite a normal CA-125 level. When used in combination, CA-125 (> 35 U/mL) and OVX1 (> 10.5 U/mL) detected persistent disease in 56% of 63 patients with positive surveillance procedures, compared with 35% when CA-125 was used alone (P < .05). An elevated OVX1 level can alert oncologists to the possibility that ovarian cancer has persisted, despite the return of CA-125 to a normal range.