An alternative screening method for prostate cancer to serum prostate specific antigen

Introduction: After 23 years of follow-up, a recent long-term study by Roobol et al showed a relative reduced mortality rate of 13% and an absolute risk reduction of 0.22% in a group screened for prostate cancer (DOI: 10.1056/NEJMoa2503223). Most prostate cancers (ProC) are not lethal and the death rate is about 15% for lethal tumors versus a majority of more indolent tumors. Prostate Specific Antigen (PSA) blood test is used for screening, but within the grey zone of 4-10ng/mL the positive predictive rate is only 25%, leading to unnecessary invasive biopsies. A more effective non-invasive test would be beneficial. Methods: Self-collected, unstimulated saliva was obtained. A dot blot p87 assay was performed using Adnab-9 monoclonal antibody (mAb) with binding minus background recorded. The mAb reacts with secretory products in the GI tract usually associated with Paneth cell secretions. Results: In the figure below, in patients with ProC, the salivary p87 was significantly lower than non-cancer controls (p<0.005). We found correlations between salivary products such as blood lysozyme, blood, and stool cancer biomarkers. p87 saliva in breast cancer patients was significantly higher (0.031±0.01) than in prostate cancer patients' saliva ( p<0.031). Conclusions: Lower concentrations of salivary lysozyme have been found to be associated with other GI and hemopoietic cancers (Sun et al. https://doi.org/10.1155/2016/8701423 ). With larger numbers we hope to show that reduced levels of salivary p87, lysozyme, and other biomarkers might be able to detect more aggressive ProC, reducing unnecessary invasive procedures and anxiety.