Fig. 1

Strategy and sample selection. a A prostate gland with four cancer foci (green and orange areas) and a pelvic lymph node with metastasis marked by a purple star. Our hypothesis is that we can determine the primary focus of metastasis origin based on matching DNA methylation in the lymph node metastasis, and this in turn will represent the most aggressive cancer subclone. By determining the aggressive subclone in multifocal PCs, we will obtain groups of aggressive and non-aggressive samples, which will form the basis for developing a classifier to determine the aggressiveness of primary PC foci. b An overview of the samples from patient 41 is shown in the upper left corner. P patient, T primary tumor focus, NL tumor-negative lymph node, PL tumor-positive lymph node. The physical location of the five prostate samples and the two lymph node samples collected are shown on schematics of the dissected prostate gland (middle) and the lymphatic system (lower left corner), respectively