Fig. 1: Overview of analyzed patient material and methods.

Out of the 712 patients, 154 were excluded for the following reasons: lack of consent (n = 28), missing baseline data (n = 28), or non-compliance with AS protocol inclusion criteria (n = 44) or AS termination criteria (no treatment despite protocol-based disease reclassification (n = 43), or treatment due to personal choice without protocol-based disease reclassification (n = 11)). Among the 558 patients included, a total of 1102 biopsies and 109 TURP procedures were performed, yielding at least 3454 tumour-containing tissue blocks (for 26 procedures, the exact number of tumour-containing tissue blocks was unknown and was assumed to be “1”). Out of these, at least 257 tissue blocks were either from procedures performed after material collection had terminated (May 2022), but before follow-up data was collected (May 2023), were missing from the archive or had no remaining tumour tissue. A total of 3197 tumour-containing tissue blocks from 1012 biopsies and 103 TURP procedures were scheduled for DNA ploidy and PTEN immunohistochemistry analyses. DNA ploidy analysis using monolayers was attempted in 2269 cases, while DNA ploidy analysis using tissue sections was performed on all 3197 tissue blocks. A combined DNA ploidy status was determined using both monolayers and tissue sections, with preference given to monolayer DNA ploidy if available; otherwise, tissue section DNA ploidy was used. AS active surveillance, TURP transurethral resection of the prostate, VHT Vestfold Hospital Trust.