Impact of Adjuvant Chemotherapy on Breast Cancer Survival: A Real-World Population.

Background: The impact of adjuvant chemotherapy on breast cancer prognosis has been demonstrated in randomized trials, but its impact is unknown in real-world populations. The aim of this study was to evaluate the effect of adjuvant chemotherapy on the survival of breast cancer patients in an unselected population.
Methods: This prospective cohort study included 32,502 women treated at the Institut Curie between 1981 and 2008 for a first invasive breast cancer without metastasis. The patients were matched based on their propensity score to receive adjuvant chemotherapy.
Results: The matching generated a subsample of 9,180 patients with an overlapping propensity score. In the group without chemotherapy, the overall survival (OS) rates at 5 and 10 years of follow-up were 87.6% (95% CI [86.7-88.6]) and 75.0% (95% CI [73.6-76.5]), respectively, versus 92.1% (95% CI [91.3-92.9]) and 81.9% (95% CI [80.6-83.2]), respectively, in the chemotherapy group. Distant disease-free survival (DDFS) was significantly improved in the five first years (absolute benefit of 3.5%). In a multivariate analysis, adjuvant chemotherapy was associated with better OS (HR = 0.75, 95% CI [0.69-0.83], p<0.0001) and DDFS (HR = 0.82, 95% CI [0.75-0.90], p<0.0001).
Conclusion: Adjuvant chemotherapy significantly improves OS and DDFS rates in an unselected population, in accordance with previous results reported by randomized trials.