Potential screening tests for ovarian cancer include transvaginal ultrasound (TVU) and the serum cancer antigen (CA) 125 assay. Several biomarkers with potential application to ovarian cancer screening are under development but have not yet been validated or evaluated for efficacy in early detection and mortality reduction.
Bimanual pelvic examination is a part of the routine pelvic examination. The sensitivity and specificity of the pelvic examination are not characterized, but examination generally detects advanced disease.[1,2]
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The Pap test may occasionally detect malignant ovarian cells, but it is not sensitive (reported sensitivity of 10%-30%) and has not been evaluated for the early detection of ovarian cancer. Another method of detection, cytologic examination of peritoneal lavage obtained by culdocentesis, is technically difficult, is uncomfortable for the patient, has low sensitivity for detecting early-stage disease, and has not been evaluated for screening.[1,3]
TVU has been proposed as a screening method for ovarian cancer because of its ability to reliably measure ovarian size and detect small masses. The benefit of ultrasonography for the early detection of ovarian cancer and reduction in mortality has not been evaluated in controlled studies. The Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO) is an ongoing randomized clinical trial evaluating the efficacy of annual TVU in combination with CA 125 tests to reduce ovarian cancer mortality.
An estimate of the false-positive rate associated with screening women aged 55 to 74 years is available from the initial four rounds of screening of women who participated in the PLCO and who were randomly assigned to be screened with TVU and serum CA 125 concentrations.[5,6] Among the 39,115 women randomly assigned to the screening arm, 34,261 were eligible for screens because they had not had a prior oophorectomy. Among these women, 89% had at least one screen during the four rounds of screening. The following TVU results were classified as abnormal (positive): "ovarian volume greater than 10 cm3; cyst volume greater than 10 cm3; any solid area or papillary projection extending into the cavity of a cystic ovarian tumor of any size; or any mixed (solid/cystic) component within a cystic ovarian tumor."[5,6] The screen positivity rates decreased slightly from 4.6% at the prevalent (baseline screen) to 2.9% at the fourth round of screening. The positive predictive value (PPV) of TVU was relatively constant over the screening rounds ranging from 0.7% to 1.1%.
Accurate estimates of sensitivity and specificity are difficult to obtain because few studies have conducted adequate follow-up to identify all cases. The U.K. Collaborative Trial of Ovarian Cancer Screening (UKCTOCS) published results from their prevalent screen. The ultrasound screening arm had several levels of screening and possible referral strategies: an abnormal scan resulted in a repeat scan in 6 to 8 weeks, and if still abnormal, referral was made for a clinical assessment. Of 53 total cancers (screen-detected and interval cancers in the following year), 45 were screened positive by ultrasound (two abnormal scans) for a sensitivity of 84.9%. For invasive cancer, the sensitivity was 75%. Specificity of the ultrasound screening arm was calculated at 98.2%.