Biochemical activity induced by a germline variation in KLK3 (PSA) associates with cellular function and clinical outcome in prostate cancer.

Genetic variation at the 19q13.3 KLK locus is linked with prostate cancer susceptibility. The non-synonymous KLK3 SNP, rs17632542 (c.536T>C; Ile163Thr-substitution in PSA) is associated with reduced prostate cancer risk, however, the functional relevance is unknown. Here, we identify that the SNP variant-induced change in PSA biochemical activity as a previously undescribed function mediating prostate cancer pathogenesis. The 'Thr' PSA variant led to small subcutaneous tumours, supporting reduced prostate cancer risk. However, 'Thr' PSA also displayed higher metastatic potential with pronounced osteolytic activity in an experimental metastasis in-vivo model. Biochemical characterization of this PSA variant demonstrated markedly reduced proteolytic activity that correlated with differences in in-vivo tumour burden. The SNP is associated with increased risk for aggressive disease and prostate cancer-specific mortality in three independent cohorts, highlighting its critical function in mediating metastasis. Carriers of this SNP allele had reduced serum total PSA and a higher free/total PSA ratio that could contribute to late biopsy decisions and delay in diagnosis. Our results provide a molecular explanation for the prominent 19q13.3 KLK locus, rs17632542 SNP, association with a spectrum of prostate cancer clinical outcomes.

Prostate cancer polygenic risk score and prediction of lethal prostate cancer.

Polygenic risk scores (PRS) for prostate cancer incidence have been proposed to optimize prostate cancer screening. Prediction of lethal prostate cancer is key to any stratified screening program to avoid excessive overdiagnosis. Herein, PRS for incident prostate cancer was evaluated in two population-based cohorts of unscreened middle-aged men linked to cancer and death registries: the Västerbotten Intervention Project (VIP) and the Malmö Diet and Cancer study (MDC). SNP genotypes were measured by genome-wide SNP genotyping by array followed by imputation or genotyping of selected SNPs using mass spectrometry. The ability of PRS to predict lethal prostate cancer was compared to PSA and a commercialized pre-specified model based on four kallikrein markers. The PRS was associated with incident prostate cancer, replicating previously reported relative risks, and was also associated with prostate cancer death. However, unlike PSA, the PRS did not show stronger association with lethal disease: the hazard ratio for prostate cancer incidence vs. prostate cancer metastasis and death was 1.69 vs. 1.65 in VIP and 1.25 vs. 1.25 in MDC. PSA was a much stronger predictor of prostate cancer metastasis or death with an area-under-the-curve of 0.78 versus 0.63 for the PRS. Importantly, addition of PRS to PSA did not contribute additional risk stratification for lethal prostate cancer. We have shown that a PRS that predicts prostate cancer incidence does not have utility above and beyond that of PSA measured at baseline when applied to the clinically relevant endpoint of prostate cancer death. These findings have implications for public health policies for delivery of prostate cancer screening. Focusing polygenic risk scores on clinically significant endpoints such as prostate cancer metastasis or death would likely improve clinical utility.

Genome-wide association study identifies novel single nucleotide polymorphisms having age-specific effect on prostate-specific antigen levels.

BACKGROUND: Testing for prostate-specific antigen (PSA) levels in blood are widely used and associated with prostate cancer risk and outcome. After puberty, PSA levels increase by age and multiple single nucleotide polymorphisms (SNPs) have been found to be associated with PSA levels. However, the relationship between the effects of SNPs and age on PSA remains unknown. METHODS: To test for SNP × age interaction, we conducted a genome-wide association study using 2394 men without prostate cancer diagnosis from Malmö, Sweden as a discovery set and 2137 men from the eMERGE study (USA) for validation. Linear regression was used to identify significant interactions between SNP and age (p < 1 × 10-4 for discovery, p < .05 for validation). RESULTS: The 15 SNPs from three different loci (8p11.22, 8p12, 3q25.31) are found to have age-specific effect on PSA levels. Expression quantitative trait loci (eQTLs) analysis shows that 12 SNPs from 3q25.31 locus affect the expression level of three genes: KCNAB1, SLC33A1, PLCH1. CONCLUSIONS: Our results suggest that SNPs may have age-specific effect on PSA levels, which provides new direction to study genetic markers for PSA.

Genome-wide Scan Identifies Role for AOX1 in Prostate Cancer Survival.

BACKGROUND: Most men diagnosed with prostate cancer have low-risk cancers. How to predict prostate cancer progression at the time of diagnosis remains challenging. OBJECTIVE: To identify single nucleotide polymorphisms (SNPs) associated with death from prostate cancer. DESIGN, SETTING, AND PARTICIPANTS: Blood samples from 11 506 men in Sweden were collected during 1991-1996. Of these, 1053 men were diagnosed with prostate cancer and 245 died from the disease. Stage and grade at diagnosis and outcome information were obtained, and DNA from all cases was genotyped. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: A total of 6 126 633 SNPs were tested for association with prostate-cancer-specific survival time using a Cox proportional hazard model, adjusted for age, stage, and grade at diagnosis. A value of 1×10-6 was used as suggestive significance threshold. Positive candidate SNPs were tested for association with gene expression using expression quantitative trait locus analysis. RESULTS AND LIMITATIONS: We found 12 SNPs at seven independent loci associated with prostate-cancer-specific survival time. One of 6 126 633 SNPs tested reached genome-wide significance (p<5×10-8) and replicated in an independent cohort: rs73055188 (p=5.27×10-9, per-allele hazard ratio [HR]=2.27, 95% confidence interval [CI] 1.72-2.98) in the AOX1 gene. A second SNP reached a suggestive level of significance (p<1×10-6) and replicated in an independent cohort: rs2702185 (p=7.1×10-7, per-allele HR=2.55, 95% CI=1.76-3.69) in the SMG7 gene. The SNP rs73055188 is correlated with AOX1 expression levels, which is associated with biochemical recurrence of prostate cancer in independent cohorts. This association is yet to be validated in other ethnic groups. CONCLUSIONS: The SNP rs73055188 at the AOX1 locus is associated with prostate-cancer-specific survival time, and AOX1 gene expression level is correlated with biochemical recurrence of prostate cancer. PATIENT SUMMARY: We identify two genetic markers that are associated with prostate-cancer-specific survival time.

Twenty-year Risk of Prostate Cancer Death by Midlife Prostate-specific Antigen and a Panel of Four Kallikrein Markers in a Large Population-based Cohort of Healthy Men.

BACKGROUND: Prostate-specific antigen (PSA) screening reduces prostate cancer deaths but leads to harm from overdiagnosis and overtreatment. OBJECTIVE: To determine the long-term risk of prostate cancer mortality using kallikrein blood markers measured at baseline in a large population of healthy men to identify men with low risk for prostate cancer death. DESIGN, SETTING, PARTICIPANTS: Study based on the Malmö Diet and Cancer cohort enrolling 11 506 unscreened men aged 45-73 yr during 1991-1996, providing cryopreserved blood at enrollment and followed without PSA screening to December 31, 2014. We measured four kallikrein markers in the blood of 1223 prostate cancer cases and 3028 controls. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Prostate cancer death (n=317) by PSA and a prespecified statistical model based on the levels of four kallikrein markers. RESULTS AND LIMITATIONS: Baseline PSA predicted prostate cancer death with a concordance index of 0.86. In men with elevated PSA (≥2.0ng/ml), predictive accuracy was enhanced by the four-kallikrein panel compared with PSA (0.80 vs 0.73; improvement 0.07; 95% confidence interval 0.04, 0.10). Nearly half of men aged 60+ yr with elevated PSA had a four-kallikrein panel score of <7.5%, translating into 1.7% risk of prostate cancer death at 15 yr-a similar estimate to that of a man with a PSA of 1.6ng/ml. Men with a four-kallikrein panel score of ≥7.5% had a 13% risk of prostate cancer death at 15 yr. CONCLUSIONS: A prespecified statistical model based on four kallikrein markers (commercially available as the 4Kscore) reclassified many men with modestly elevated PSA, to have a low long-term risk of prostate cancer death. Men with elevated PSA but low scores from the four-kallikrein panel can be monitored rather than being subject to biopsy. PATIENT SUMMARY: Men with elevated prostate-specific antigen (PSA) are often referred for prostate biopsy. However, men with elevated PSA but low scores from the four-kallikrein panel can be monitored rather than being subject to biopsy.

Association Between Lead Time and Prostate Cancer Grade: Evidence of Grade Progression from Long-term Follow-up of Large Population-based Cohorts Not Subject to Prostate-specific Antigen Screening.

BACKGROUND: Lead time (LT) is of key importance in early detection of cancer, but cannot be directly measured. We have previously provided LT estimates for prostate cancer (PCa) using archived blood samples from cohorts followed for many years without screening. OBJECTIVE: To determine the association between LT and PCa grade at diagnosis to provide an insight into whether grade progresses or is stable over time. DESIGN, SETTING, AND PARTICIPANTS: The setting was three long-term epidemiologic studies in Sweden including men not subject to prostate-specific antigen (PSA) screening. The cohort included 1041 men with PSA of 3-10 ng/ml at blood draw and subsequently diagnosed with PCa with grade data available. OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Multivariable logistic regression was used to predict high-grade (Gleason grade group ≥2 or World Health Organization grade 3) versus low-grade PCa at diagnosis in terms of LT, defined as the time between the date of elevated PSA and the date of PCa diagnosis with adjustment for cohort and age. RESULTS AND LIMITATIONS: The probability that PCa would be high grade at diagnosis increased with LT. Among all men combined, the risk of high-grade disease increased with LT (odds ratio 1.13, 95% confidence interval [CI] 1.10-1.16; p<0.0001), with no evidence of differences in effect by age group or cohort. Higher PSA predicted shorter LT by 0.46 yr (95% CI 0.28-0.64; p<0.0001) per 1 ng/ml increase in PSA. However, there was no interaction between PSA and grade, suggesting that the longer LT for high-grade tumors is not simply related to age. Limitations include the assumption that men with elevated PSA and subsequently diagnosed with PCa would have had biopsy-detectable PCa at the time of PSA elevation. CONCLUSIONS: Our data support grade progression, whereby following a prostate over time would reveal transitions from benign to low-grade and then high-grade PCa. PATIENT SUMMARY: Men with a longer lead time between elevated prostate-specific antigen and subsequent prostate cancer diagnosis were more likely to have high-grade cancers at diagnosis.

Strategy for detection of prostate cancer based on relation between prostate specific antigen at age 40-55 and long term risk of metastasis: case-control study.

OBJECTIVE: To determine the association between concentration of prostate specific antigen (PSA) at age 40-55 and subsequent risk of prostate cancer metastasis and mortality in an unscreened population to evaluate when to start screening for prostate cancer and whether rescreening could be risk stratified. DESIGN: Case-control study with 1:3 matching nested within a highly representative population based cohort study. SETTING: Malmö Preventive Project, Sweden. PARTICIPANTS: 21,277 Swedish men aged 27-52 (74% of the eligible population) who provided blood at baseline in 1974-84, and 4922 men invited to provide a second sample six years later. Rates of PSA testing remained extremely low during median follow-up of 27 years. MAIN OUTCOME MEASURES: Metastasis or death from prostate cancer ascertained by review of case notes. RESULTS: Risk of death from prostate cancer was associated with baseline PSA: 44% (95% confidence interval 34% to 53%) of deaths occurred in men with a PSA concentration in the highest 10th of the distribution of concentrations at age 45-49 (≥ 1.6 µg/L), with a similar proportion for the highest 10th at age 51-55 (≥ 2.4 µg/L: 44%, 32% to 56%). Although a 25-30 year risk of prostate cancer metastasis could not be ruled out by concentrations below the median at age 45-49 (0.68 µg/L) or 51-55 (0.85 µg/L), the 15 year risk remained low at 0.09% (0.03% to 0.23%) at age 45-49 and 0.28% (0.11% to 0.66%) at age 51-55, suggesting that longer intervals between screening would be appropriate in this group. CONCLUSION: Measurement of PSA concentration in early midlife can identify a small group of men at increased risk of prostate cancer metastasis several decades later. Careful surveillance is warranted in these men. Given existing data on the risk of death by PSA concentration at age 60, these results suggest that three lifetime PSA tests (mid to late 40s, early 50s, and 60) are probably sufficient for at least half of men.

Evaluation of multiple risk-associated single nucleotide polymorphisms versus prostate-specific antigen at baseline to predict prostate cancer in unscreened men.

BACKGROUND: Although case-control studies have identified numerous single nucleotide polymorphisms (SNPs) associated with prostate cancer, the clinical role of these SNPs remains unclear. OBJECTIVE: Evaluate previously identified SNPs for association with prostate cancer and accuracy in predicting prostate cancer in a large prospective population-based cohort of unscreened men. DESIGN, SETTING, AND PARTICIPANTS: This study used a nested case-control design based on the Malmö Diet and Cancer cohort with 943 men diagnosed with prostate cancer and 2829 matched controls. Blood samples were collected between 1991 and 1996, and follow-up lasted through 2005. MEASUREMENTS: We genotyped 50 SNPs, analyzed prostate-specific antigen (PSA) in blood from baseline, and tested for association with prostate cancer using the Cochran-Mantel-Haenszel test. We further developed a predictive model using SNPs nominally significant in univariate analysis and determined its accuracy to predict prostate cancer. RESULTS AND LIMITATIONS: Eighteen SNPs at 10 independent loci were associated with prostate cancer. Four independent SNPs at four independent loci remained significant after multiple test correction (p<0.001). Seven SNPs at five independent loci were associated with advanced prostate cancer defined as clinical stage≥T3 or evidence of metastasis at diagnosis. Four independent SNPs were associated with advanced or aggressive cancer defined as stage≥T3, metastasis, Gleason score≥8, or World Health Organization grade 3 at diagnosis. Prostate cancer risk prediction with SNPs alone was less accurate than with PSA at baseline (area under the curve of 0.57 vs 0.79), with no benefit from combining SNPs with PSA. This study is limited by our reliance on clinical diagnosis of prostate cancer; there are likely undiagnosed cases among our control group. CONCLUSIONS: Only a few previously reported SNPs were associated with prostate cancer risk in the large prospective Diet and Cancer cohort in Malmö, Sweden. SNPs were less useful in predicting prostate cancer risk than PSA at baseline.

A panel of kallikrein marker predicts prostate cancer in a large, population-based cohort followed for 15 years without screening.

BACKGROUND: Prostate-specific antigen (PSA) has modest specificity for prostate cancer. A panel of four kallikrein markers (total PSA, free PSA, intact PSA, and kallikrein-related peptidase 2) is a highly accurate predictor of biopsy outcome. The clinical significance of biopsy-detectable cancers in men classified as low-risk by this panel remains unclear. METHODS: The Malmö Diet and Cancer study is a population-based cohort of 11,063 Swedish men aged 45 to 73 providing a blood sample at baseline during 1991-1996. The Swedish Cancer Registry was used to identify 943 men diagnosed with prostate cancer by December 31, 2006. PSA testing was low. We assessed the predictive accuracy of our published statistical model to predict subsequent prostate cancer diagnosis in men with a total PSA level of 3.0 ng/mL or more at baseline. RESULTS: Compared with total PSA and age, the full kallikrein panel enhanced the predictive accuracy for clinically diagnosed prostate cancer (concordance index 0.65 vs. 0.75; P < 0.001). For every 1,000 men with a total PSA level of 3 ng/mL or more at baseline, the model would classify as high-risk 131 of 152 (86%) of the cancer cases diagnosed clinically within 5 years; 421 men would be classified as low-risk by the panel and recommended against biopsy. Of these, only 2 would be diagnosed with advanced prostate cancer (clinical T3-T4 or metastases) within 5 years. CONCLUSIONS: Men with a PSA level of 3 ng/mL or more but defined as low-risk by the panel of four kallikrein markers are unlikely to develop incurable prostate cancer. IMPACT: Use of the panel to determine referral to biopsy could substantially reduce the number of unnecessary prostate biopsies.

Prediction of significant prostate cancer diagnosed 20 to 30 years later with a single measure of prostate-specific antigen at or before age 50.

BACKGROUND: We previously reported that a single prostate-specific antigen (PSA) measured at ages 44-50 was highly predictive of subsequent prostate cancer diagnosis in an unscreened population. Here we report an additional 7 years of follow-up. This provides replication using an independent data set and allows estimates of the association between early PSA and subsequent advanced cancer (clinical stage ≥T3 or metastases at diagnosis). METHODS: Blood was collected from 21,277 men in a Swedish city (74% participation rate) during 1974-1986 at ages 33-50. Through 2006, prostate cancer was diagnosed in 1408 participants; we measured PSA in archived plasma for 1312 of these cases (93%) and for 3728 controls. RESULTS: At a median follow-up of 23 years, baseline PSA was strongly associated with subsequent prostate cancer (area under the curve, 0.72; 95% CI, 0.70-0.74; for advanced cancer, 0.75; 95% CI, 0.72-0.78). Associations between PSA and prostate cancer were virtually identical for the initial and replication data sets, with 81% of advanced cases (95% CI, 77%-86%) found in men with PSA above the median (0.63 ng/mL at ages 44-50). CONCLUSIONS: A single PSA at or before age 50 predicts advanced prostate cancer diagnosed up to 30 years later. Use of early PSA to stratify risk would allow a large group of low-risk men to be screened less often but increase frequency of testing on a more limited number of high-risk men. This is likely to improve the ratio of benefit to harm for screening.

Prostate specific antigen concentration at age 60 and death or metastasis from prostate cancer: case-control study.

OBJECTIVE: To determine the relation between concentrations of prostate specific antigen at age 60 and subsequent diagnosis of clinically relevant prostate cancer in an unscreened population to evaluate whether screening for prostate cancer and chemoprevention could be stratified by risk. DESIGN: Case-control study with 1:3 matching nested within a highly representative population based cohort study. SETTING: General population of Sweden taking part in the Malmo Preventive Project. Cancer registry at the National Board of Health and Welfare. PARTICIPANTS: 1167 men aged 60 who provided blood samples in 1981 and were followed up to age 85. MAIN OUTCOME MEASURES: Metastasis or death from prostate cancer. RESULTS: The rate of screening during the course of the study was low. There were 43 cases of metastasis and 35 deaths from prostate cancer. Concentration of prostate specific antigen at age 60 was associated with prostate cancer metastasis (area under the curve 0.86, 95% confidence interval 0.79 to 0.92; P<0.001) and death from prostate cancer (0.90, 0.84 to 0.96; P<0.001). The greater the number for the area under the curve (values from 0 to 1) the better the test. Although only a minority of the men with concentrations in the top quarter (>2 ng/ml) develop fatal prostate cancer, 90% (78% to 100%) of deaths from prostate cancer occurred in these men. Conversely, men aged 60 with concentrations at the median or lower (≤1 ng/ml) were unlikely to have clinically relevant prostate cancer (0.5% risk of metastasis by age 85 and 0.2% risk of death from prostate cancer). CONCLUSIONS: The concentration of prostate specific antigen at age 60 predicts lifetime risk of metastasis and death from prostate cancer. Though men aged 60 with concentrations below the median (≤1 ng/ml) might harbour prostate cancer, it is unlikely to become life threatening. Such men could be exempted from further screening, which should instead focus on men with higher concentrations.