MALDI TOF MSI of three prostate tissue specimens with Gleason score (GS) indicated inset, a) H&E image of serial tissue section with tumor region, as determined by an expert pathologist, outlined in black, b) segmentation map of MALDI MSI data produced via k-means clustering (k = 12), c) m/z 400.5 which is assigned as palmitoylcarnitine, d) m/z 782.7 which is assigned as PC(34:1), e) m/z 704.3, an unidentified ion which exhibits lower intensity in the tumor and f) m/z 749.1 which is assigned as PS(32:2).