KLK3 and pachyonychia congenita: In particular, and differing from previous reviews, (1) the methodology to be used for exosome analysis in PC is specifically described; (2) we specifically analyzed how exosome analysis can improve the specificity and sensitivity of the major marker used in PC diagnosis, PSA (PSA expressing exosomes); and (3) we specifically analyzed the relationship between exosomes and carbonic anhydrase expression in PC.