KLK3 and prostate cancer: This study investigated the association of widespread opportunistic prostate-specific antigen (PSA) testing with SEP measures and quantified the extent to which multilevel measures of SEP contributed to the observed spatial variation in PSA testing.<h4>Methods</h4>A population-based register study was conducted, encompassing 471 335 men aged 40 years and older without a prior prostate cancer diagnosis residing in the Stockholm region in 2016.