In situ detection of AR-V7, AR-FL, and KLK3 transcripts in CTCs of castration-resistant prostate cancer (CRPC) patients. (A) For each patient, the number and expression profile of CTCs is visualized. CTCs are represented by black circles. RCPs specific for AR-V7, AR-FL, and KLK3 are visualized as yellow, red, and green spots, respectively. Based on the background in healthy controls, only cells with ≥1 KLK3 RCPs/cell, ≥2 AR-V7 RCPs/cell or ≥3 AR-FL RCPs/cell were rated as CTCs. (B) Overview of in-situ-analyzed cells on a CellCollector (patient 16). DAPI-stained nuclei are shown in gray. Scale bar = 100 μm. Representative CTCs from patients 15 (C), 6 (D), 16 (E), and 11 (F) are depicted in more detail. Scale bar = 10 μm. AR-V7-, AR-FL-, and KLK3-specific RCPs appear as yellow, red, and green spots, respectively, and are marked by arrowheads. White arrowheads indicate unspecific staining patterns (fluorescent in all channels or signals outside a cell).