The UK NICE guidelines define men suitable for AS as having the following characteristics: clinical stage T1c; a Gleason score of 3 + 3; a PSA density of < 0.15 ng/mL/mL; and cancer in < 50 % of their total number of biopsy cores with < 10 mm of any core involved (http://guidance.nice.org.uk/CG175) [5]. This evidence concerns the gene KLK3 and cancer.