Here, using a highly specific mouse monoclonal antibody 7C10-C5 against methyl-L309 of PP2A-C, we provide evidence for this unique post-translational modification in prostate cancer tissues where its loss was associated with biochemical recurrence and metastasis, highlighting its potential utility as a prognostic biomarker in prostate cancer. The gene discussed is PPP2CA; the disease is prostate carcinoma.