Purpose: To determine the prognostic significance of deoxyribonucleic acid (DNA) ploidy in comparison to pretreatment prostate specific antigen (PSA) and other prognostic factors for patients with adenocarcinoma of the prostate treated with external beam radiotherapy.
Methods and materials: Paraffin-embedded prostatic adenocarcinoma material was obtained from patients treated from 1987-1991. Sufficient histologic material for flow cytometric DNA content analysis was obtained from 86 patients and adequate histograms were obtained from 76 of these. The DNA histogram profiles were classified as diploid, tetraploid, or aneuploid. Median patient follow-up was 36 months.
Results: There were 54 patients with diploid tumors, and 22 with nondiploid tumors (11 tetraploid and 11 aneuploid). Since the disease outcome for tetraploid and aneuploid tumors was the same, these were pooled (nondiploid tumors). The distribution of diploidy and nondiploidy correlated with pretreatment PSA (p < 0.0005) and grade (p = 0.055), but not with stage, pretreatment prostatic acid phosphatase, transurethral resection, pretreatment serum testosterone, or age. In actuarial univariate analyses, DNA ploidy was a significant predictor of outcome for local failure, distant metastases, any clinical relapse, rising PSA, and rising PSA and/or relapse. Ploidy was not a significant predictor of overall survival, although there were only six deaths. Diploidy predicted for improved outcome, for example, 34.6% incidence of a rising PSA and/or relapse at 4 years compared to 76.9% with nondiploidy (p < 0.0001). An actuarial univariate analysis of other potential prognostic factors using the composite endpoint of rising PSA and/or relapse also revealed pretreatment PSA, grade, pretreatment prostatic acid phosphatase, stage, and serum testosterone to be significant predictors of outcome. In Cox proportional hazards analysis, pretreatment PSA, DNA ploidy, and grade were the only independent prognostic factors for disease outcome using the composite endpoint.
Conclusion: DNA ploidy is an independent predictor of outcome in patients with Stages T1-T3 prostate cancer treated with definitive external beam radiotherapy.