That both PTEN and 12p13 deletions showed the same inverse relationship with MTAP expression as seen for tumor cell proliferation raises the possibility that PTEN and one or several genes on 12p13 (such as the p27/KIP1 tumor suppressor) may be directly or indirectly involved in the ERG dependent switch of the MTAP role in prostate cancer. The gene discussed is PTEN; the disease is neoplasm.