Evaluation of the Patient With Prostate Cancer

Radiologic Methods

According to published reports, the accuracy of TRUS in staging of prostate cancer is variable. Although some studies have indicated that TRUS could detect an extracapsular extension of the tumor in as many as 92% of cases, a large and more recent study found an accuracy of only 62%.^[2,17,18] Invasion of the SVs can be detected by TRUS.^[19,20] TRUS can quantify tumor volume, guide biopsy needles to the capsule and SV, and calculate PSA density.^[19,20] The disadvantages associated with TRUS include observer dependence and a high rate of false-negative results in the presence of isoechoic or hyperechoic tumors.^[21] In spite of the existing controversy, most believe that it has a 64% accuracy, a 78% to 99% specificity, and a 59% to 87% sensitivity in the staging of prostate cancer patients. Currently, TRUS is almost universally performed as an initial staging step because it is an integral part of the procedure used to obtain biopsies for the diagnosis of prostate cancer.^{[22,23,24,25,26]}

The overall accuracy of CT in staging localized tumors is only 61%, which is only slightly higher than that of clinical staging. The sensitivity of CT scans in detecting involved lymph nodes ranges from 25% to 93%, specificity from 85% to 100%, and accuracy from 77% to 93%.^{[27,28,29,30]} But the cost of performing a CT is high ($400-$800/patient). Thus, CT is a procedure not indicated for routine staging of localized prostate cancer. These conclusions are similar to those drawn in a study by Wolf and colleagues,^[31] who used a decision analysis tree to calculate cost-effectiveness of pelvic CT. They found that it would cost $50,661 per patient (with positive lymph nodes) who would benefit by avoiding RP, if all prospective cases underwent staging by pelvic CT or MRI.^[31,32]

Getty and colleagues^[33] have evaluated the usefulness of MRI in prostate cancer staging. Nine experienced radiologists evaluated a total of 200 cases from 4 medical centers. They measured, both singly and in combination, the reliability of each of the 4 diagnostic variables: age, PSA level, Gleason tumor grade, and MRI findings. The accuracy of staging with the individual variables (age, 0.58; PSA level, 0.74; Gleason grade, 0.73; MRI findings, 0.74) increased as the variables were optimally merged. Combination of all 4 variables resulted in an accuracy of 0.86. In a clinically important subset of 69 cases for which PSA level and Gleason grade together were inconclusive for the purpose of staging, the addition of MRI findings resulted in an increase in accuracy (from 0.55 to 0.73).

In another study, a total of 73 patients with biopsy-documented prostate carcinoma were examined with MRI before RP. The overall accuracy of endorectal coil MRI in defining local tumor stage was 82% (60 of 73 patients). The sensitivity and specificity of endorectal coil MRI in diagnosing capsular penetration were 95% and 82%, respectively. SV invasion was detected with a 80% sensitivity and a 93% specificity. Authors concluded that endorectal coil MRI was an accurate method for local staging of prostate cancer.

Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein defined by the monoclonal antibody 7E11.C5, which forms the basis of an in vivo diagnostic-imaging agent, In¹¹¹ capromab pendetide, used for identification of metastatic prostate cancer. Lymph nodes that have been invaded by prostate cancer cells appear as "hot spots" on the test. Khan and associates have studied and evaluated the ability of immunoscintigraphy with this radiolabeled monoclonal antibody to differentiate between local and distant recurrence in 181 men with post-RP biochemical recurrence.Immunoscintigraphy revealed disease in 60% of the patients with interpretable scans. Current results of this technology appear promising and its exact role in the management of prostate cancer will be established as the data mature.^{[34,35,36,37,38,39,40,41]}

Radionuclide scintigraphy is an integral component of prostate cancer staging. In the past, 23% of all patients reported normal by skeletal radiography had bone metastasis on scintigraphy. One disadvantage of bone scintigraphy is that although it is highly sensitive, it is nonspecific, and radiographic confirmation is required for the positive findings (8% false-negative results).^{[42,43,44,45,46,47,48]} The cost of a bone scintigraphy is between $46 and $138 for Medicare patients.

Several authors have demonstrated that if PSA was less than 20 ng/mL, the probability of a positive bone scintigraphy was extremely low.^{[21,22,23,49]} These authors reported that the median serum PSA concentration in patients with positive bone scintigraphy was 158 ng/mL, whereas men with negative bone scintigraphy had a median serum PSA value of 11.3 ng/mL (P < .0001). No patient with a serum PSA value of less than 15 ng/mL had a positive bone scintigraphy. Oesterling^[50] advocated avoidance of bone scintigraphy in these patients, which could translate into $38 million a year in savings for the United States healthcare system. We, however, have found positive bone scans in rare patients with a Gleason score of 7 or higher and a serum PSA less than 10 ng/mL. Therefore, we advocate bone scans in patients with a Gleason score of 7 or more, regardless of serum PSA.^[51]

© 2000 Medscape

Cite this: Evaluation of the Patient With Prostate Cancer - Medscape - Sep 14, 2000.