Different prognostic effect of postoperative chemoradiation therapy on diploid and nondiploid high-risk rectal cancers

Abstract

PURPOSE: DNA ploidy has been shown to play a role in the response to cytotoxic therapy in a variety of malignancies, including breast cancer and melanoma. However, the importance of DNA ploidy in rectal cancer is unknown. The aim of the present study was to determine whether ploidy status might be associated with response to postoperative chemoradiation in TNM Stages II to III rectal cancer. METHODS: This retrospective study analyzed data from 229 patients with TNM Stages II to III rectal cancer who underwent resection between 1979 and 1984. The ploidy status and treatment modalities in relation to outcome were assessed. RESULTS: The recurrence-free ten-year survival rate was 52.2 percent for patients with diploidy and 50.5 percent for patients with nondiploidy (P=0.99). The ten-year survival rates for patients with diploidy and patients with nondiploidy were 55 and 19 percent (P=0.016) in the chemoradiation group, and 51 and 60 percent (P=0.15) in the nonchemoradiation group, respectively. In the chemoradiation group, DNA nondiploidy was associated with an increased recurrence rate (83.3vs. 50.0 percent;P=0.001). The interaction between DNA nondiploidy and chemoradiation remained important in predicting outcome in the Cox regression model. Factors independently correlated with a worse outcome included Stage IIIb (relative risk, 2.9; 95 percent confidence interval, 1.7–5;P=0.0001), perineural invasion (relative risk, 2.5; 95 percent confidence interval, 1.6–4,P=0.0001), distal tumor (relative risk, 1.7; 95 percent confidence interval, 1.1–2.7,P=0.014), and nondiploidy with chemoradiation (relative risk, 2.9; 95 percent confidence interval, 1.2–7.2,P=0.0213). CONCLUSIONS: These findings suggest that DNA nondiploidy is inversely correlated with long-term outcome among patients with high-risk rectal cancer receiving chemoradiation.