Cancers 2010, 2, 1125-1154; doi:10.3390/cancers2021125 OPEN ACCESS cancers ISSN 2072-6694 www.mdpi.com/journal/cancers Review Markers for Detection of Prostate Cancer Raymond A. Clarke 1, Horst J. Schirra 2, James W. Catto 3, Martin F. Lavin 4,5 and Robert A. Gardiner 5,* 1 Prostate Cancer Institute, Cancer Care Centre, St George Hospital Clinical School of Medicine, University of New South Wales, Kogarah, NSW 2217, Australia; E-Mail: [email protected] 2 School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane QLD, 4072, Australia; E-Mail: [email protected] 3 Academic Urology Unit and Institute for Cancer Studies, University of Sheffield, Royal Hallamshire Hospital, Sheffield S10 2JF, UK; E-Mail: [email protected] 4 Queensland Institute of Medical Research, Radiation Biology and Oncology, Brisbane, QLD 4029, Australia; E-Mail: [email protected] 5 University of Queensland Centre for Clinical Research, Brisbane, Australia * Author to whom correspondence should be addressed; E-Mail: [email protected]. Received: 22 March 2010; in revised form: 2 June 2010 / Accepted: 3 June 2010 / Published: 4 June 2010 Abstract: Early detection of prostate cancer is problematic, not just because of uncertainly whether a diagnosis will benefit an individual patient, but also as a result of the imprecise and invasive nature of establishing a diagnosis by biopsy. Despite its low sensitivity and specificity for identifying patients harbouring prostate cancer, serum prostate specific antigen (PSA) has become established as the most reliable and widely-used diagnostic marker for this condition. In its wake, many other markers have been described and evaluated. This review focuses on the supporting evidence for the most prominent of these for detection and also for predicting outcome in prostate cancer. Keywords: prostate cancer; biomarker; detection Cancers 2010, 2 1126 1. Introduction Prostate cancer (PCa) is now the most commonly diagnosed internal cancer in the western world and the second most lethal male malignancy. Prior to clinical availability of a blood test for prostate specific antigen (PSA) in the mid 1980s, most PCa patients were diagnosed with more advanced disease. Advances in surgical and radiation therapies now result in cure for a proportion of patients who would not have benefitted from combination PSA/digital rectal examination (DRE)-based detection in the past. However, from a public health perspective, indiscriminate PSA population screening cannot be justified because of the low sensitivity and specificity of this blood test in identifying cancer, amongst other concerns [1]. Furthermore, there is prevailing uncertainty on the basis of the PSA blood test as to who will benefit from treatment with curative intent [2–5]. Recognition of these shortcomings has focussed research into markers to detect the presence of PCa and, more importantly, to try to discriminate between those patients harbouring indolent as opposed to aggressive disease including those for whom any form of local therapy will not prevent subsequent declaration of metastases. There is a clinical imperative in being able to identify those who do and do not have PCa since, apart from the obvious advantage from detecting and treating the condition at the earliest stage possible, the diagnostic process itself is not without its problems. Suspicion of the presence of PCa, alerted as a result of an abnormal serum PSA and/or and abnormal DRE, requires an invasive procedure to provide histological confirmation with biopsies (usually >12) almost always obtained via imaging with a transrectal ultrasound (TRUS) probe to ensure spatial positioning of biopsy needles. The majority of men who have prostatic biopsies do not have PCa diagnosed but continue to have raised serum PSA levels with ongoing concerns of a possible undetected PCa due to the imprecise nature of both the PSA test and TRUS biopsies. US Medicare-SEER analyses 1993 to 2001 indicated that, among men whose first recorded biopsy did not detect cancer, the likelihood of undergoing subsequent biopsies was 11.6% at 1 year and 38% at 5 years [6]. In addition, although the dreaded complication of life-threatening sepsis is fortunately uncommon but reported to be increasing [7], ~50% experience lesser symptoms after TRUS biopsy so diagnosing PCa remains problematic for many reasons. Consequently, it is not surprising that the need to be able to detect prostate cancer by a simple and reliable approach which can be repeated easily over time, is a diagnostic priority in the western world. 2. Scope of the Review The strengths and weaknesses of PSA in the detection of PCa have been examined and published extensively and, since the topic has been reviewed very recently by Roobol et al. [8], who comprehensively examined the relevant medical literature with respect to the risk of developing PCa, this dissertation will not re-visit this marker. These authors reported that, despite its limitations, published evidence indicates that total serum PSA is the single most significant clinically-used predictive factor for identifying men at increased risk for PCa. Total PSA was superior to percentage free PSA, PSA velocity and Human kallikrein 2 (hK2), the most studied kallikrein protein after PSA (hK3) itself. A suspicious DRE, a family history of PCa, the presence of high grade prostatic intraepithelial neoplasia (HGPIN) or atypical small acinar proliferation (ASAP) and black ethnicity Cancers 2010, 2 1127 also were reported to be important predictive factors. For men of screening age (50 to 70 years) a serum PSA of greater than 1.5 ng/mL has been found to indicate a greater than average risk up to 8 years (7.5-times greater risk vs. 1.5 ng/mL or less) for developing PCa [8]. In terms of diagnosing established PCa, PSA cut-offs are useful with the likelihood of men harbouring PCa greater the higher the level of serum PSA. However, it is important to note that PSA is a continuous variable and that a proportion of patients with low serum PSA levels <4 ng/mL have PCa of clinical significance [9]. Histological interpretation too has advanced with the Gleason scoring criteria agreed upon at the WHO ISUP consensus meeting in 2005 [10,11] being more useful clinically than those criteria with Gleason grading used previously. Much has been published in the Uro-pathology literature in relation to histological nuances in addition to describing a range of tissue biomarkers for PCa characterisation. These include apoptotic factors such as p53 and Bcl-2, the androgen receptor (AR), signal transduction factors within the EGF receptor family, cell cycle regulators exemplified by c-Myc, p16, p27, pRb and Ki67, cell adhesion and cohesion factors and factors involved in neo-angiogenesis, such as vascular endothelial growth factor (VEGF), VEGF receptors and nitric oxide [12,13] Histopathology will not be addressed further nor will imaging adjuncts to biopsy. However, in interpreting the value of diagnostic biomarkers from biological fluids, which is the subject of this review, accurate histology and appropriate targeting with biopsy needles are essential. It is particularly important to be aware that the diagnostic biopsy reference on which biological fluid biomarkers are judged is deficient, varying with sites targeted and numbers of biopsies obtained, ranging in one study from 31.7% for sextant biopsies to 38.7%, 41.5%, and 42.5% for 12, 18 and 21 cores respectively in a study of 1000 patients [14]. Accurately determining the presence of disease is surprisingly difficult. Autopsy studies permit exhaustive and comprehensive scrutiny of the prostate histologically but are flawed in terms of clinical relevance for epidemiological reasons. True incidence derived from more epidemiologically-vetted clinical trials is almost non-existent given the rarity of complete cross-sectional ‘end of study biopsies’. Sakr found in autopsy studies that, for the third through to the eighth decades of life, the incidence of PCa in a cohort of 1051 subjects was 7, 23, 39, 44, 65 and 72% [15]. Haas et al. [16] performed 18 core biopsies on autopsy prostates from 164 men who had no history of PCa. They reported that six-core biopsies were taken from each of the mid peripheral zone (MPZ), the lateral peripheral zone (LPZ), and the central zone (CZ). PCa was present in 47 (29%) prostates. Of the 47 cancers detected, 20 were clinically significant according to histologic criteria. Biopsies from the CZ did not detect any cancer that was not present in biopsies from either the MPZ or LPZ. The sensitivities of biopsies from the MPZ for clinically significant and insignificant cancer were 55% (95% CI = 32% to 77%) and 11%, respectively, compared with 80% and 33% for those from the MPZ and LPZ combined. In a single institutional study, Djavan et al. [17] found in an assessment of repeat biopsies that PCa was present in 22% (231/1051), 10% (83/820), 5% (36/737) and 5% (4/94) of first, second, third and fourth biopsies. Together with others, these studies illustrate the fact that the reference by which the sensitivity and specificity of biomarkers are judged is well short of perfect and this deficiency also should be borne in mind in assessing the predictive values of potential biomarkers. Cancers 2010, 2 1128 3. Sources for Biomarker Analyses A number of tissue/fluid sources and approaches have been employed in the quest to develop a non- invasive diagnostic test for PCa. These range from analysing tears [18] to changes in the odour of urine detected by dogs [19] but, in terms of commonly studied sources, prostatic fluid and blood have received most attention. Patient acceptance of venesection for taking samples of blood (for analysis as whole blood or serum) and providing urine is extremely high and laboratory staff are so conversant with the properties of both that they do not warrant detailed discussion in this manuscript.