Serum and Tissue Markers for Prostate Cancer

Serum and Tissue Markers for Prostate Cancer

10TH INTERNATIONAL PROSTATE CANCER UPDATE Serum and Tissue Markers for Prostate Cancer Michael K. Brawer, MD,* Martin E. Gleave, MD,† Hans Lilja, MD, PhD,‡ Martin I. Resnick, MD,§ Nelson Neal Stone, MD|| *Northwest Prostate Institute, Seattle; †University of British Columbia, Vancouver; ‡Lund University, Malmo, Sweden; § Case Western Reserve University School of Medicine, Cleveland; ||Mount Sinai School of Medicine of New York University, New York The pace has quickened in the search for more cost-effective and predictive serum and tissue markers for prostate cancer. At the heart of the efforts is improved specificity in prostate-specific antigen (PSA) testing. The complexed PSA test provides improvement in test specificity similar to the free/total PSA ratio. Other novel markers, such as human kallikrein 2, show significant promise. Key words: Prostate-specific antigen • Prostatic neoplasms • Sensitivity and specificity • Tumor markers P rostate-specific antigen (PSA) continues to provide a unique opportunity for those of us in urologic oncology because it is the most important tumor marker in all of human oncology. Efforts to improve PSA testing have generally been directed toward enhancing specificity for several reasons: false-positive tests create an abundance of anxiety in patients, and they are expensive because they mandate further testing, ultrasonography, antibiotics, biopsy, and pathology charges. Enhancement in specificity results in reduced false-positive testing. Efforts to achieve this involve the use of the PSA derivatives (density, velocity, age specificity, and measurement of the isoforms of PSA). False-negative tests are also important, but less so, because prostate cancer is relatively slow-growing. PSA Derivatives PSA density (the quotient of serum PSA level divided by prostate volume) has been reported by a number of authorities to offer significant enhancement in cancer detection. The theory is that the majority of prostate volume is associated with enlargement of the transition zone with benign prostatic hyperplasia1-3; by normalizing volume, cancer specificity would be enhanced. A number of investigators have demonstrated enhanced specificity with this adjustment.3-9 Others have not been able to reproduce these findings,10 including investigators at the University of Washington who showed that using PSA density for testing was no better than using PSA alone.11 This discrepancy may have a number of etiologies, including differences in ultrasound measurement error, variability in histologic makeup in the cohort undergoing biopsy, biopsy sampling error, and PSA assay variability. The biggest factor is a problem with sampling in larger glands, with a decrease in cancer detection observed in glands larger than 55 cc (Figure).12 A number of investigators looked at the transition zone PSA density to enhance performance of PSA testing. Zlotta and colleagues13 as well as Maeda and cowork- 10 REVIEWS IN UROLOGY Supplement Serum/Tissue Markers 45 PZ Volume 40 35 30 % Yield ers14 showed enhanced performance with this measurement. Lin and others15 were unable to reproduce these results. Most clinicians have abandoned the use of PSA density in clinical practice. The age-specific PSA reference range, a PSA derivative that has been used widely, is based on the concept that an arbitrary cutoff level (for example, 4 ng/mL) may not be appropriate for all men. Oesterling and coworkers16 suggested that because PSA levels increase with advancing age, it would be better to use a lower cutoff level in younger men and a higher cutoff level in older men. He theorized that this would provide greater test sensitivity in younger men and fewer negative biopsy results in older men. Reissigl and associates17 found that age-specific cutoffs resulted in enhancement of both sensitivity and specificity in men between the ages of 45 and 59; in older men, specificity was increased and cancer detection was slightly diminished. Unfortunately, others have reported dissimilar results. Borer and associates18 observed that the majority of cancers that would be missed in men between the ages of 60 and 79 had life-threatening characteristics. The Northwest Prostate Institute (NWPI) group demonstrated in a screening study that with a cutoff of 4 ng/mL for all men, there was only a marginal increase in the positive biopsy rate and a significant reduction in cancer detection. Using US life-table figures, these researchers observed that even with the higher potential for detecting cancer in younger men using the lower cutoff levels, the net effect on the population with age-specific PSA would be a reduction in potential life years saved, compared with life years saved using the standard 4 ng/mL level cutoff. Another PSA derivative is PSA velocity (the change in PSA level over time). It stands to reason that men with cancer will have a more rapid increase in total PSA (tPSA) level over time than will men without cancer. Carter and associates,19 based on the Baltimore Longitudinal Aging Study, dem- 25 20 15 10 5 0 1 2 3 4 5 6 7 8 9 10 Decile Figure. Cancer detection rate as a function of peripheral zone (PZ) volume. Adapted with permission from Letran J et al. J Urol. 1998.12 onstrated stratification of those men with and without prostate cancer who had a PSA velocity greater than 0.75 ng/mL per year. Investigators at the University of Washington and others have been unable to reproduce the results of Carter using relatively short PSA intervals.20,21 Catalona and colleagues22 confirmed the inability to use PSA velocity in a clinically meaningful way. Carter and associates23 originally had a minimum of 7 years between determinations, which other investigators did not find useful. The authors subsequently demonstrated that PSA velocity is helpful if a minimum of 3 consecutive measurements are taken over a 2-year period. Recently, Nixon and coworkers24,25 reported a significant day-to-day variation in serum PSA levels. It is intriguing that men with cancer had less variation than men without cancer, perhaps because men with cancer have a higher proportion of PSA complexed to 1-antichymotrypsin (PSA-ACT) than men without cancer have.26,27 The clearance rate by the kidneys of the PSA-ACT complex is much slower than the clearance rate of free, noncomplexed PSA (fPSA).28 The problem with biologic variation cou- pled with laboratory variability and manufacturer assay differences probably precludes obtaining useful information from PSA velocity, except when very long intervals are used. PSA Isoforms Undoubtedly, the most exciting advance in PSA testing has been the recognition that PSA circulates not in 1 form but complexes to a number of protease inhibitors.26,29 Most of the PSA in the circulation is PSA-ACT. fPSA accounts for a much smaller amount in the circulation, although this is the major form found in the ejaculate. PSA is also bound to another proteinase inhibitor—2-macroglobulin (AMG). When enzymatically active PSA is added to serum or plasma in vitro,30 this form is difficult to measure and is not readily identified by any commercial assay because of steric hindrance of the epitopes. By contrast, the PSAAMG complex is unlikely to occur in vivo at significant levels; in preoperative, perioperative, or postoperative samples from prostatectomy-treated men with localized prostate cancer, PSA-AMG was not found at detectable concentrations.31 Little is known about Supplement REVIEWS IN UROLOGY 11 Serum/Tissue Markers continued Table 1 Diagnosis Performance at Set Levels of Sensitivity Hybritech f/tPSA Dianon fPSA/Hybritech tPSA Chiron fPSA/Hybritech tPSA Sensitivity (%) % f/t cut point Specificity (%) % f/t cut point Specificity (%) % f/t cut point Specificity (%) 2-20 ng/mL range (25 with cancer, 100 with no evidence of malignancy) 90 20 44 33 22 34 33 95 22 38 34 19 35 32 100 29 16 42 13 43 16 2-10 ng/mL range (18 with cancer, 87 with no evidence of malignancy) 90 20 45 33 23 33 38 95 22 38 34 19 35 36 100 29 15 40 15 42 21 PSA, prostate-specific antigen; f/tPSA, free/total PSA ratio. Adapted from Nixon RG et al. J Urol. 1998.38 the actual site of PSA complexation. While ACT occurs in 10- to 100-fold molar excess, it is well recognized that the fPSA occurs in a greater proportion of men without carcinoma, in contrast to the complexed form (cPSA), which occurs in a higher proportion of men with malignancy.26,27 In 1991, Stenman and associates26 demonstrated a correlation between the levels of cPSA and prostate cancer. Lilja and associates30 were the first to design an immunoassay specific for fPSA; subsequently, Christensson and coworkers27 showed that the ratio of the free-to-total PSA (f/tPSA) was lower in men with carcinoma. Luderer and coworkers32 reported confirmatory findings: f/tPSA ratio differentiated men with carcinoma from those without over the truncated range of tPSA levels between 4 and 10 ng/mL; tPSA did not differentiate men with carcinoma. Similar enhancement has been demonstrated by Higashihara and associates33 and by Chen and coworkers.34 The definitive trial of the role of f/tPSA was reported by Catalona and associates.35 This 7-institution study evaluated men with benign glands and tPSA levels between 4 and 10 ng/mL. These investigators observed that with an f/tPSA ratio of less than 25%, the sensitivity was 95% and the specificity enhancement over tPSA was 20%. 12 REVIEWS IN UROLOGY Supplement That is to say, 1 of 5 negative biopsy results could be avoided if the physician was willing to miss 5% of cancers. Despite the tremendous advance of f/tPSA, several concerns exist. One problem is the limited in vitro stability of fPSA, particularly in serum. This necessitates very strict sample handling, including separation of serum/plasma from the blood cells within a few hours of sample collection and analysis of serum on the same day as sample collection; otherwise, the sample has to be kept frozen (ideally at –70°C for longterm storage) to provide optimal analysis.36 Maybe the biggest problem is lack of uniformity between different manufacturers in achieving a similar result using the same patient specimen. This bias is compounded when a quotient is obtained. For example, if the fPSA level found by a manufacturer slightly overreads that reported in the literature and the tPSA level is slightly less than a literature-based value, these manufacturer differences would compound the differences between the literature results and clinical testing. Considerable bias in tPSA levels between manufacturers37,38 and also in fPSA levels38 has been observed (Table 1). More recently, Roth and associates37 demonstrated considerable bias when the free and total assays of 1 manufacturer were compared with those of oth- er manufacturers (Table 2). These data show significant variability when different manufacturers’ assays are employed. Clinicians must be aware of the assays that their laboratories are using. Ideally, laboratory personnel should define the performance of each fPSA and tPSA assay in their patient setting before the test is used clinically. Complexed PSA Problems associated with the f/tPSA ratio, particularly assay variability and the increased magnitude of error when the quotient is derived, would be obviated if the cPSA were available. The reason assays to measure fPSA and tPSA levels were developed was because of difficulty in achieving a specific assay for cPSA. It had been demonstrated that the ACT form of PSA is more specific for cancer. Recently, the Bayer Corporation developed a specific PSA assay directed against cPSA. In the initial evaluation of this series at NWPI, investigators studied 300 men who had undergone ultrasoundguided prostate needle biopsy. They compared the results of the Bayer Immuno-1 cPSA assay with the Hybritech Tandem R and total assays. As expected, the mean, tPSA, and cPSA levels were higher in men with cancer, and the f/tPSA ratio was significantly lower. Performance characteristics for Serum/Tissue Markers Table 2 Comparison of the Sensitivity and Specificity of tPSA and the f/tPSA Ratio in Patients in BPH and Prostate Cancer Groups Assay ACS: 180 PSA 2 and fPSA Enzymum PSA and fPSA Tandem-R PSA and fPSA Sensitivity (%) 100 95 90 100 95 90 100 95 90 Specificity (%) tPSA 0 10 25 0 5 24 1 7 17 Specificity (%) f/tPSA 0 17 54 0 7 32 1 22 31 Cut point tPSA (ng/mL) 0.02 1.7 3.3 0.02 1.1 3 0.4 2.1 3.4 Cut point f/tPSA (%) 90 25 15 100 43 23 52 25 21 PSA, prostate-specific antigen; tPSA, total PSA; f/tPSA, free/total PSA ratio; BPH, benign prostatic hyperplasia; fPSA, free PSA. Adapted from Roth HJ et al. PCPD. 1998.37 Table 3 Specificity of the Cut Point Values of the Different PSA Assays at Selected Sensitivities (Entire tPSA Range) tPSA Sensitivity (%) 80 85 90 95 97.5 100 Cut point (ng/mL) 4.11 3.86 3.4 3.06 2.28 1 cPSA Specificity (%) 35.6 31.1 25.3 21.8 12.9 3.1 Cut point (ng/mL) 3.98 3.34 2.94 2.52 1.67 0.89 f/tPSA Specificity (%) 51.6 38.7 33.8 26.7 14.7 6.2 Cut point (%) 19 22 24 28 32 67 Specificity (%) 46.2 32.4 26.2 15.6 8.9 0 PSA, prostate-specific antigen; tPSA, total PSA; cPSA, complexed PSA; f/tPSA, free/total PSA ratio. Adapted from Brawer MK et al. Urology. 1998.51 Table 4 Specificity of tPSA and cPSA and the f/tPSA Ratio for Samples Within the Sensitivity Range of 80% to 95% tPSA Sensitivity (%) 80 85 90 95 Cut point (ng/mL) 4.64 4.33 3.99 3.06 cPSA Specificity (%) 41 33 28 18 Cut point (ng/mL) 4.09 3.79 3.40 2.75 Specificity (%) 46 41* 32 24* f/tPSA Cut point (%) 17.1 18.9 20.9 23.9 Specificity (%) 52*† 42* 31 23* PSA, prostate-specific antigen; tPSA, total PSA; cPSA, complexed PSA; f/tPSA, free/total PSA ratio. *Significantly different from tPSA. † Significantly different from cPSA. Adapted with permission from Brawer MK et al. J Urol. 2000.39 Supplement REVIEWS IN UROLOGY 13 Serum/Tissue Markers continued tPSA, cPSA, and f/tPSA are shown in Table 3. At the 95% sensitivity level, the specificity of tPSA was 21.8%. A cPSA level of 2.52 demonstrated an enhanced specificity of 26.7%. It is intriguing that the f/tPSA ratio in this series, with a cutoff of 28%, resulted in a reduction of specificity to only 15.6%. To further understand the utility of cPSA, Brawer and colleagues39 expanded the Seattle series by incorporating patients evaluated at Johns Hopkins University by Alan Partin, MD, as well as a small cohort derived from a multicenter screening trial that is under way. In this investigation, 272 men with carcinoma detected on ultrasound-guided biopsy were contrasted with 385 men with benign findings. Again, the Bayer cPSA and the Hybritech tPSA and fPSA assays were used. Tables 4 and 5 demonstrate the significant findings. At the 95% sensitivity level, tPSA provided 18% specificity at a cutoff of 3.06 ng/mL. The cPSA afforded a significant increase: 24% specificity at a cutoff value of 2.75 ng/mL. The f/tPSA ratio at this sensitivity level and a cutoff of 23.9% provided 23% specificity. The greater enhancement in test performance with cPSA is shown in the more truncated range of 4 to 10 ng/mL for tPSA, as demonstrated in Table 5. Table 6 summarizes the literature comparing cPSA with tPSA and the f/tPSA ratio. In most studies, cPSA provides essentially the equivalent performance of the f/tPSA ratio, but there are 2 exceptions. In the study by Jung and associates,40 cPSA performed significantly worse than f/tPSA. Of note in this series: the investigators did a significant subset analysis to obviate the effect of tPSA between those men with and without cancer. This data manipulation may have introduced significant bias into their report. The study by Stamey and Yemoto41 is different in a number of ways from the studies of other investigators. The Stanford group required 2 biopsies before a patient was considered free of disease. Moreover, patients had to have a minimum of 5 mm of cancer to be included in the cancer cohort. The biggest discrepency, however, between the Stanford experience and that of the NWPI group is the difference in tPSA levels. In the NWPI studies, the tPSA level is significantly higher in men with malignancy—a finding that is certainly in the majority of reports. For undetermined reasons, in the Stanford series, there was no difference in tPSA level between those with and without malignancy. This may have introduced a significant bias and may, in part, reflect the similarity of the results of the Stamey and Jung studies. The NWPI group is currently doing a prospective evaluation of the role of cPSA in early detection of screening. To date, 2361 men have been evaluat- ed. Table 7 shows the significant findings. Using a cutoff of 4 ng/mL for tPSA, 401 men (17%) would require biopsy. With cPSA and a cutoff of 3.75 ng/mL, 311 men (13.2%) would require biopsy (a reduction in biopsy rate of 22.4%). In 91 men who have had biopsy performed because of a tPSA higher than 4 ng/mL, cancer was detected in 39.6%. Using cPSA with a cutoff of 3.75 ng/mL, 2 malignancies would be missed and 11% of benign biopsies would be avoided. These data from a prospective screening cohort demonstrate for the first time that cPSA provides nearly equivalent sensitivity and significantly enhanced specificity, compared with tPSA. The cPSA test has been improved for the monitoring of men with established malignancy. FDA approval is pending for its use in early detection. Because cPSA is equivalent to tPSA for monitoring and staging purposes and seems to show enhancement in early detection, it is likely that this analyte will be the PSA test of choice in the future. Kallikrein One of the newer advances in serum markers for prostate cancer is human kallikrein 2 (hK2). This serine protease has extensive sequence identity to PSA (hK3). hK2 can convert the inactive zymogen (proPSA) to enzymatic PSA. Further, this conversion of proPSA to Table 5 Specificity of tPSA and cPSA and the f/tPSA Ratio Within the Sensitivity Range of 80% to 95% for Samples in the tPSA Range of 4 to 10 ng/mL tPSA Sensitivity (%) 80 85 90 95 Cut point (ng/mL) 5.06 4.67 4.42 4.24 cPSA Specificity (%) 30 21 11 7 Cut point (ng/mL) 4.37 4.19 3.94 3.7 f/tPSA Ratio Specificity (%) 37 31* 25 18* PSA, prostate-specific antigen; tPSA, total PSA; cPSA, complexed PSA; f/tPSA, free/total PSA ratio. *Significantly different from tPSA. † Significantly different from cPSA. Adapted with permission from Brawer MK et al. J Urol. 2000.39 14 REVIEWS IN UROLOGY Supplement Cut point (%) 17.1 18.9 20.5 23.3 Specificity (%) 48*† 34* 25* 17* Serum/Tissue Markers Table 6 cPSA in Biopsy Series Author Brawer51 Number of men 225 No cancer 75 Analyte tPSA f/tPSA cPSA Specificity @ 90% sensitivity (%) 25 26 34 Specificity @ 95% sensitivity (%) 22 16 27 Brawer39 3853 2374 tPSA f/tPSA cPSA 28 31 32 18 23 24 Croal52 58 21 tPSA f/tPSA cPSA 52 54 60 43 52 57 Jung40 401 402 tPSA f/tPSA cPSA 18 55 25 — — — Maeda53 114 23 tPSA f/tPSA cPSA 24 18 27 13 18 15 Sokoll54 60 76 tPSA f/tPSA cPSA 40 — 42 35 — 37 Stamey41 90 70 tPSA f/tPSA cPSA 12 47 14 4 29 10 PSA, prostate-specific antigen; cPSA, complexed PSA; tPSA, total PSA; f/tPSA, free/total PSA ratio 1 Selected from 89 patients to simulate overlapping tPSA values. 2 Selected from 144 patients to simulate overlapping tPSA values. 3 Includes 225 cases from Brawer.51 4 Includes 75 cases from Brawer.51 53 91% specificity reported. 54 96% specificity reported active enzyme is a prerequisite for the formation of the PSA-ACT complex and of other complexed forms of PSA.42 A unique feature of hK2 is that it seems to be increasingly expressed in transformed epithelium as compared with PSA, which begins to be less translated as cancer becomes more aggressive. In an evaluation of men from the Goteborg screening study, hK2 was evaluated in conjunction with fPSA and tPSA.43 Of the 604 men with tPSA levels higher than 3 ng/mL who accepted an invitation for further evaluation, including digital rectal examination, transrectal ultrasonography, and sextent biopsy, 144 received a diagnosis of prostatic carcinoma. Medium values for all analyte combinations as well as t test comparison statistically showed significantly higher hK2 levels as well as tPSA levels in men with a diagnosis of cancer. As expected, the f/tPSA ratio was significantly lower in men with malignancy. The optimal performing equation was that derived from the value of hK2 times tPSA divided by fPSA. In this group, the receiver operating character area under the curve was 0.81. This was significantly greater than that obtained with tPSA but not significantly greater than the f/tPSA ratio. However, at high sensitivity levels, as shown in Table 8, calculated value provided the best specificity at clinically relevant sensitivities. Obviously, more data are necessary before this can be clinically Supplement REVIEWS IN UROLOGY 15 Serum/Tissue Markers continued Table 7 tPSA and cPSA in a Screening Population Age 50 - 59 60 - 69 70 - 79 ≥ 80 All Number 692 786 685 198 2361 tPSA mean (SD) 1.75 (2.51) 2.63 (4.17) 2.74 (2.72) 3.01 (4.53) 2.43 (0.41) tPSA median 1 1.7 1.9 1.65 1.5 cPSA mean (SD) 1.39 (2.29) 2.21 (4.98) 2.13 (2.33) 2.36 (4.24) 1.96 (3.6) PSA median 0.7 1.29 1.39 1.22 1.08 PSA, prostate-specific antigen; tPSA, total PSA; cPSA, complexed PSA. recommended. Another study of men with localized prostate cancer treated with radical prostatectomy, done in Hamburg, Germany, showed that the hK2 levels were significantly lower in men with organconfined disease than in those with extraprostatic extension44; tPSA levels were not significantly different. Both these and several recent studies reported by Recker and colleagues45 show that very sensitive and specific hK2 measurements may provide an intriguing potential advance in PSA testing. One obvious liability is the considerable potential quotient bias, as described above, when 3 analytes are measured. In addition, the cost may be prohibitive. Advances in Prostate Cancer Staging Despite tremendous efforts in enhancement of prostate cancer staging, few tests have proved clinically useful. Compounding this are 2 major factors: (1) a significant decrease in stage of cancer at diagnosis has been realized, not only in the United States, but also in most nations that have adopted PSA testing; (2) the heterosensitivity of the tumor itself makes sampling a critical issue. Particularly apparent has been the decrease in pelvic lymph node metastasis. One concern is that patients thought to be free of nodal metastasis on routine pathologic examination may harbor occult disease. Suggestive of this is the observation that a high percentage of men with negative nodes experiences biochemical failure.46 More accurate assessment of appropriate candidates for pelvic lymph node examination and refinements in pathologic analysis are needed. A number of authorities have used immunohistochemical and other molecular tools to evaluate pelvic lymph nodes and have demonstrated that these enhanced sensitivity methods show significant detection of occult disease.47-49 The reverse transcriptase–polymerase chain reaction (RT-PCR) has been evaluated in a number of clinical settings in men with prostatic carcinoma. Using primers (PSA or prostatespecific membrane antigen [PSMA]), this method detects as few as 1 tumor cell in 10 million lymphocytes. Recent designs of quantitative RT-PCR procedures detecting 50 to 107 PSA mRNA copies50 show that the mRNA content in each cell varies from 800 to 10,000 mRNA copies. Appropriate cut points remain to be established. So far, the qualitative RT-PCR procedures have been of little use clinically in the examination of circulating red blood cells. Use of RT-PCR in the evaluation of pelvic lymph nodes has been surpris- Table 8 Median Sensitivity, Specificity, and Positive Predictive Value for 604 Men Who Had Biopsy With tPSA Levels ≥ 3 ng/mL* Sensitivity tPSA tPSA/fPSA hK2 x fPSA/tPSA 75 47 (31) 63† (39) 74† (47) % Specificity at given level of sensitivity PPV (%) 80 85 38 (29) 31 (28) 57† (37) 51† (35) † 59 (38) 52† (36) 90 20 (26) 43† (33) 45† (34) PSA, prostate-specific antigen; tPSA, total PSA; PPV, positive preditive value; fPSA, free PSA; hK2, human kallikrein 2. *Significant differences in analytical performance using the combination of hK2, fPSA, and tPSA (P < .05) are denoted † for increased performance compared with tPSA. Adapted from Becker C et al. Urology. 2000.43 16 REVIEWS IN UROLOGY Supplement Serum/Tissue Markers Table 9 Comparison Analysis of PSA/iPSA and PSMA RT-PCR Assay Results Between Control Male Lymph Node Tissues and Pelvic Lymph Nodes of 109 N0 Prostate Cancer Patients* Lymph nodes Control (%) PC (%) P value Number 29 109 iPSA-positive 0 (0) 30 (28) < .001 iPSA-negative 29 (100) 79 (72) PSMA-positive 0 (0) 76 (70) .001 PSMA-negative 29 (100) 33 (30) PSA, prostate-specific antigen; iPSA, nested assay; PSMA, prostate-specific membrane antigen; RT-PCR, reverse transcriptase-polymerase chain reaction; N0, node zero; PC, prostate cancer. *iPSA represents the nested assay; PSMA represents the use of outer primers only. Adapted from Ferrari AC et al. J Natl Cancer Inst. 1997.49 Table 10 Distribution of N0 Patients by iPSA and PSMA RT-PCR Positive Signals in Pelvic Lymph Node Tissue RNA Risk Factors at Presentation Gleason score <7 ≥7 Number 32 75 iPSA-positive 4 (13%) 26 (35%) P = .019 PSMA-positive 20 (63%) 54 (72%) P = .33 N0, node zero; iPSA, nested assay; PSMA, prostate-specific membrane antigen; RT-PCR, reverse transcriptase-polymerase chain reaction. Adapted from Ferrari AC et al. J Natl Cancer Inst. 1997.49 ing. Ferrari and associates49 (Tables 9 and 10) demonstrated a significant increase in identifying pelvic lymph node metastasis with RT-PCR as compared with histologic examinations. These investigators used control lymph nodes derived from cadaver specimens and those obtained from node dissections in men with prostatic carcinoma. There was no nested (inner primer set) PSA-mRNA expression in lymph nodes of the 29 control specimens. Nested PSMA expression was detected in 34% of control lymph nodes. Use of an outer primer set for PSMA (a less sensitive assay) resulted in all control lymph nodes being negative. Among 109 specimens from men undergoing pelvic lymph node dissection, 77% were positive for PSA or PSMA, 70% were positive for PSMA, and 28% were positive for PSA. These data suggest that PSA-mRNA was highly specific for disease, while PSMA-mRNA was not. The data regarding biochemical failure rates suggest a trend favoring patients with negative assays for PSA and RTPCR. Longer follow-up is necessary before definitive statements can be made. The conclusion from this preliminary study, however, suggests that the use of RT-PCR signals for PSA in lymph nodes may provide early detection of micrometastasis. ■ References 1. Stamey TA, Yang N, Hay AR, et al. Prostate-specific antigen as a serum marker for adenocarcinoma of the prostate. N Engl J Med. 1987;317:909916. 2. Babaian RJ, Fritsche HA, Evans RB. 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