Background: DNA ploidy is a significant prognostic factor in patients with prostate cancer. Using DNA/nuclear protein flow cytometry, a subpopulation of tumors with near-diploid DNA is identifiable. The prognostic significance 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 classified as either diploid (n = 30), near-diploid (n = 24), or nondiploid (n = 22, tetraploid and aneuploid). Median follow-up time was 36 months.
Results: Diploid tumors were associated with a significantly better actuarial outcome at 4 years, compared with near-diploid tumors, using either biochemical relapse (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 between diploid and near-diploid neoplasms regarding actuarial local control, freedom from metastasis, freedom from clinical relapse, or overall survival time. A Cox proportional hazards model, using the composite end point of a rising PSA or relapse, was performed with ploidy categorized as diploid, near-diploid, and nondiploid; pretreatment PSA, DNA ploidy, and tumor grade were found to be independent prognostic factors. When ploidy was categorized as diploid or near-diploid (nondiploid tumors excluded), pretreatment serum PSA and DNA ploidy were independent predictors of outcome. Ploidy remained an independent prognostic factor even when nondiploid tumors were excluded.
Conclusions: These data show that patients who have near-diploid tumors have an intermediate prognosis between the more favorable diploid tumors and the less favorable nondiploid tumors.