Impact of Relative Dose Intensity (RDI) on Survival in Non-Metastatic Breast Cancer: Nigerian Experience

Background: This study was initiated to determine practices patterns in adjuvant chemotherapy for non-metastatic breast cancer and to examine the relationship between received dose intensity (RDI) and survival in patients with breast cancer Nigeria. Methods: Our study was a retrospective analysis of patients with breast cancer recruited from 2012 and 2015. A total of 204 patients were initially entered into the study, 102 were lost to follow-up leaving 102 patients who were suitable for the survival analysis. Survival time was calculated from 106 days, the scheduled end of chemotherapy. Results: The total average RDI for patients was 74%. Over the 204 patients that were reviewed, 144 (70.6%) had some reduction of RDI. This subgroup had an average RDI of 63%. On average, 79% of the intended dose of chemotherapy was given. The time to completion of chemotherapy was 1.33 times that specified by the protocol. Dose delays an overall reduction was mainly attributed to intolerability and financial constraints. Survival by RDI showed a significant decrease in survival rate for patients with RDI of >49% (Hazard Ratio = 3.473, 95% CI 1.21 - 9.91, P = 0.020); RDI of 50% - 59% (Hazard Ratio = 3.916, 95% CI 1.01 - 15.18, P = 0.048); RDI of 60% - 69% (Hazard Ratio = 4.462, 95% CI 1.65 - 12.03, P = 0.003) compared with patients who received an RDI of 100%. Although associated with poorer prognosis, there were no significant changes in the survival rate for patients with RDI of 70% - 79% (Hazard Ratio = 1.667, 95% CI 0.56 - 4.96, P = 0.359); RDI of 80% - 89% (Hazard Ratio = 1.620, 95% CI 0.47 - 5.53, P = 0.441); RDI 90% - 99% (Hazard Ratio = 1.590, 95% CI 0.53 - 4.73, P = 0.405) compared with patients who received an RDI of 100%. Conclusion: This study provides evidence that decreased RDI of <70% in non-metastatic breast cancer patients is strongly associated with decreased overall survival.