Canine arginine esterase, a kallikrein detected in the prostatic fraction, found to be the protein in the higher abundance in canine seminal plasma [24], is an immunological marker for assessing the normal function of the prostate gland [66]; it is similar to the prostatic specific antigen, which in men is an important marker for prostate cancer [67]. The gene discussed is KLK3; the disease is prostate cancer.