Radioimmunoscintigraphy with Tc-99m-labelled SM3 in differentiating malignant from benign adnexal masses

Objective: Ultrasound scanning, serum CA125 and menopausal status have previously been combined in a risk of malignancy index for the differential diagnosis of adnexal masses. Although this approach has greater accuracy than either individual tests or clinical assessment, it has a significant false positive and false negative rate. Efforts have been directed at refining differential diagnosis and this study assessed the role of radioimmunoscintigraphy using the stripped mucin 3 (SM3) antibody that has a 17-fold greater uptake in malignant than benign ovarian tumours in vitro. Design: Prospective study of patients with a pelvic mass using radioimmunoscintigraphy. Setting: Department of Nuclear Medicine of St Bartholomew's Hospital in collaboration with Cancer Network. Population: A total of 93 patients with pelvic masses were recruited for this study of which 32 had ovarian cancer and 61 had benign lesions. Methods: Radioimmunoscintigraphy was performed with Tc-99m-labelled SM3 (600 MBq), anterior and posterior pelvis imaged at 10 minutes and at 4 and 24 hours and evaluated with change detection analysis and probability mapping. Main outcome measures: Sensitivity and specificity of radioimmunoscintigraphy for ovarian cancer. Results: Radioimmunoscintigraphy had a sensitivity for ovarian cancer of 84% (27 true positive and 5 false negatives) and a specificity of 87% (53 true negatives and 8 false positives) giving a negative predictive value of 91%. Conclusion: These results suggest that radioimmunoscintigraphy could be used to reduce the number of false positive findings in a strategy to refine differential diagnosis of the pelvic mass.