BACKGROUND: Lynch syndrome is a rare familial cancer syndrome caused by pathogenic variants in the mismatch repair genes MLH1, MSH2, MSH6, or PMS2, that cause predisposition to various cancers, predominantly colorectal and endometrial cancer. Data are emerging that pathogenic variants in mismatch repair genes increase the risk of early-onset aggressive prostate cancer. The IMPACT study is prospectively assessing prostate-specific antigen (PSA) screening in men with germline mismatch repair pathogenic variants. Here, we report the usefulness of PSA screening, prostate cancer incidence, and tumour characteristics after the first screening round in men with and without these germline pathogenic variants. METHODS: The IMPACT study is an international, prospective study. Men aged 40-69 years without a previous prostate cancer diagnosis and with a known germline pathogenic variant in the MLH1, MSH2, or MSH6 gene, and age-matched male controls who tested negative for a familial pathogenic variant in these genes were recruited from 34 genetic and urology clinics in eight countries, and underwent a baseline PSA screening. Men who had a PSA level higher than 3·0 ng/mL were offered a transrectal, ultrasound-guided, prostate biopsy and a histopathological analysis was done. All participants are undergoing a minimum of 5 years' annual screening. The primary endpoint was to determine the incidence, stage, and pathology of screening-detected prostate cancer in carriers of pathogenic variants compared with non-carrier controls. We used Fisher's exact test to compare the number of cases, cancer incidence, and positive predictive values of the PSA cutoff and biopsy between carriers and non-carriers and the differences between disease types (ie, cancer vs no cancer, clinically significant cancer vs no cancer). We assessed screening outcomes and tumour characteristics by pathogenic variant status. Here we present results from the first round of PSA screening in the IMPACT study. This study is registered with ClinicalTrials.gov, NCT00261456, and is now closed to accrual. FINDINGS: Between Sept 28, 2012, and March 1, 2020, 828 men were recruited (644 carriers of mismatch repair pathogenic variants [204 carriers of MLH1, 305 carriers of MSH2, and 135 carriers of MSH6] and 184 non-carrier controls [65 non-carriers of MLH1, 76 non-carriers of MSH2, and 43 non-carriers of MSH6]), and in order to boost the sample size for the non-carrier control groups, we randomly selected 134 non-carriers from the BRCA1 and BRCA2 cohort of the IMPACT study, who were included in all three non-carrier cohorts. Men were predominantly of European ancestry (899 [93%] of 953 with available data), with a mean age of 52·8 years (SD 8·3). Within the first screening round, 56 (6%) men had a PSA concentration of more than 3·0 ng/mL and 35 (4%) biopsies were done. The overall incidence of prostate cancer was 1·9% (18 of 962; 95% CI 1·1-2·9). The incidence among MSH2 carriers was 4·3% (13 of 305; 95% CI 2·3-7·2), MSH2 non-carrier controls was 0·5% (one of 210; 0·0-2·6), MSH6 carriers was 3·0% (four of 135; 0·8-7·4), and none were detected among the MLH1 carriers, MLH1 non-carrier controls, and MSH6 non-carrier controls. Prostate cancer incidence, using a PSA threshold of higher than 3·0 ng/mL, was higher in MSH2 carriers than in MSH2 non-carrier controls (4·3% vs 0·5%; p=0·011) and MSH6 carriers than MSH6 non-carrier controls (3·0% vs 0%; p=0·034). The overall positive predictive value of biopsy using a PSA threshold of 3·0 ng/mL was 51·4% (95% CI 34·0-68·6), and the overall positive predictive value of a PSA threshold of 3·0 ng/mL was 32·1% (20·3-46·0). INTERPRETATION: After the first screening round, carriers of MSH2 and MSH6 pathogenic variants had a higher incidence of prostate cancer compared with age-matched non-carrier controls. These findings support the use of targeted PSA screening in these men to identify those with clinically significant prostate cancer. Further annual screening rounds will need to confirm these findings. FUNDING: Cancer Research UK, The Ronald and Rita McAulay Foundation, the National Institute for Health Research support to Biomedical Research Centres (The Institute of Cancer Research and Royal Marsden NHS Foundation Trust; Oxford; Manchester and the Cambridge Clinical Research Centre), Mr and Mrs Jack Baker, the Cancer Council of Tasmania, Cancer Australia, Prostate Cancer Foundation of Australia, Cancer Council of Victoria, Cancer Council of South Australia, the Victorian Cancer Agency, Cancer Australia, Prostate Cancer Foundation of Australia, Asociación Española Contra el Cáncer (AECC), the Instituto de Salud Carlos III, Fondo Europeo de Desarrollo Regional (FEDER), the Institut Català de la Salut, Autonomous Government of Catalonia, Fundação para a Ciência e a Tecnologia, National Institutes of Health National Cancer Institute, Swedish Cancer Society, General Hospital in Malmö Foundation for Combating Cancer.
The IMPACT study is funded by Cancer Research UK (grant references C5047/A21332, C5047/ A13232, and C5047/A17528) and The Ronald and Rita McAulay Foundation and the National Institute for Health Research (NIHR) support to the Biomedical Research Centre at The Institute of Cancer Research and Royal Marsden NHS Foundation Trust. JO is supported by Cancer Research UK Programme Grant (reference C8161/A16892). We thank Mr and Mrs Jack Baker for supporting the study in NorthShore University HealthSystem, Evanston, IL, USA. We acknowledge funding from the NIHR to the Biomedical Research Centre at The Institute of Cancer Research and the Royal Marsden NHS Foundation Trust, London, at Manchester University Foundation Trust (IS-BRC-1215-20007), the Oxford Biomedical Research Centre Program, and the Cambridge Clinical Research Centre, NIHR Cambridge Biomedical Research Centre. DGE is supported by the Manchester NIHR Biomedical Research Centre (IS-BRC-1215-20007). We acknowledge that, in Australia, this project was co-funded by Cancer Council Tasmania and Cancer Australia (grant number 1006349 [2011–13]), Prostate Cancer Foundation of Australia (grant number PCFA PRO4 ), Cancer Councils of Victoria and South Australia (grant number 400048 [2006–08]), the Victorian Cancer Agency Clinical Trial Capacity CTCB08_14, Cancer Australia and Prostate Cancer Foundation of Australia (2014–16; grant number 1059423), and Translational grants EOI09_50. We acknowledge the support of the Asociación Española Contra el Cáncer (AECC), the Instituto de Salud Carlos III (organismo adscrito al Ministerio de Economía y Competitividad), “Fondo Europeo de Desarrollo Regional (FEDER), una manera de hacer Europa” (PI10/01422, PI13/00285, PIE13/00022, PI16/00563, JR18/00011 and CIBERONC), and the Institut Català de la Salut and Autonomous Government of Catalonia (2009SGR290, 2014SGR338 and PERIS Project MedPerCan). We acknowledge funding support from Fundação para a Ciência e a Tecnologia to the IPO Porto study (project grant PTDC/DTP-PIC/1308/2014 to MRT and fellowship grant SFRH/BD/116557/2016). We acknowledge funding support to HL from the National Institutes of Health National Cancer Institute with a Cancer Center Support Grant to Memorial Sloan Kettering Cancer Center (P30 CA008748), a SPORE grant in Prostate Cancer (P50 CA092629), Swedish Cancer Society (Cancerfonden 20 1354 PjF), and General Hospital in Malmö Foundation for Combating Cancer. This research is sponsored and coordinated by The Institute of Cancer Research (London, UK) and reviewed by the Committee for Clinical Research at the Royal Marsden NHS Foundation Trust and West Midlands – Edgbaston REC. The funding bodies supported recruitment but did not have any input into study design, the collection, analysis, or interpretation of data, in the writing of the report, or in the decision to submit the paper for publication. We are indebted to all the men who took part in this study. We are grateful to the past and present members of the Data and Safety Monitoring Committee (appendix p 2). We acknowledge the contribution of past members of the IMPACT Steering Committee.
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