An essential event in the progression of adenocarcinoma is the loss of organized epithelial attachment (both to the basement membrane and to adjoining epithelial cells). The E-cadherin cell adhesion molecule has an established function in maintaining normal phenotype and tissue homeostasis, and loss of E-cadherin function has been implicated in tumorigenesis. Aberrations in E-cadherin are associated with prostate cancer progression; however, these aberrations are not simply a result of prodigious allelic loss. We have previously demonstrated a novel posttranslational truncation within the cytosolic domain of native Mr 120,000 E-cadherin to a membrane-bound Mr 97,000 species. We hypothesize that truncation of E-cadherin is an inactivating event that is significantly increased in localized prostate tumors and that it represents a novel molecular event that may distinguish prostate cancer from adjacent normal tissue. E-cadherin was characterized by Western blot analysis in matched normal and cancer tissue from 18 prostate cancer patients. Imaging and densitometry software were used to quantify the truncation of E-cadherin by measuring the ratio of Mr 97,000 E-cadherin to Mr 120,000 E-cadherin, which was significantly increased in the tumor aspect of the prostate gland. Herein, we report the first experiment comparing case-matched human normal and cancerous prostate tissue in the context of E-cadherin truncation.