KLK3 and Familial prostate cancer: The method development studies showed the viability of multiplexed fluorescence ICC for detection of PrAD‐CTCs with a wide range of EpCAM, PanCK, AMACR, and PSMA expression levels (Figure S2), as well as other key aspects including specificity of marker combination to prostate cancer (Figure S3), absence of PrAD CTCs in benign prostate conditions (Table S1), and the ability of the test to detect CTCs irrespective of patient age (Figure S4), serum PSA levels (Figure S5), Gleason Score (Figure S6), or extent of disease (Figure S7).