Near-Diploidy: A New Prognostic Factor for Clinically Localized Prostate Cancer Treated with External Beam Radiation Therapy

Background. DNA ploidy is a significant prognostic factor in patients with prostate cancer. Using DNA/nu-clear protein flow cytometry, a subpopulation of tumors with near-diploid DNA is identifiable. The prognostic sig-nificance of near-diploidy was examined. Methods. Paraffin-embedded formalin fixed prostate tumor tissue from patients treated at M. D. Anderson Cancer Center with external beam radiation therapy was processed for DNA/nuclear protein flow cytometry. All patients had pretreatment and follow-up serum prostate specific antigen (PSA) levels. Seventy-six specimens were suitable for flow cytometric analysis. Tumors were clas-sified as either diploid (n = 30), near-diploid (n = 24), or nondiploid (n = 22, tetraploid and aneuploid). Median fol-low-up time was 36 months. Results. Diploid tumors were associated with a signif-icantly better actuarial outcome at 4 years, compared with near-diploid tumors, using either biochemical re-lapse (rising PSA) or a composite end point of a rising PSA or clinical relapse (16 % versus 52 % relapse, P < 0.05, log-rank). Moreover, patients who had nondiploid tumors had the worst prognosis (77 % relapse, composite end point). No significant difference was observed be-tween diploid and near-diploid neoplasms regarding ac-tuarial local control, freedom from metastasis, freedom from clinical relapse, or overall survival time. A Cox proportional hazards model, using the composite en