Disseminated Tumor Cells Predict Efficacy of Regional Nodal Irradiation in Early Stage Breast Cancer

Abstract

Disseminated tumor cells (DTCs) collect in the bone marrow and indicate micrometastatic spread. We previously reported that DTCs could be a predictive factor for the efficacy of regional node irradiation (internal mammary nodes [IMNs]/supra- and infraclavicular nodes [SCNs]). In this article, we report the long-term results (>10years) on the impact of DTC status in early stage breast cancer. Patients with localized breast cancer were eligible for inclusion in this prospective cohort. DTCs were obtained from a medullary iliac crest sample performed before any primary therapy. DTC status was prospectively assessed by pathologists. Irradiation volumes were defined per standard of care. Cumulative incidence rates and hazard ratios were obtained using both Cox and Fine-Gray models. Interaction tests were performed to confirm the predictive value of DTC status in a multivariate analysis. Six hundred twenty patients with localized breast cancer were included. Overall, 94 patients (15.2%) were DTC-positive. After a median follow-up of 11.7years, 47 patients (7.6%) experienced locoregional relapse. DTC detection was associated with a higher risk of locoregional relapse in univariate and multivariate analyses (Cox hazard ratio, 3.26; 95% confidence interval, 1.6-5.7; P=.001). In the multivariate subgroup analysis, IMN/SCN irradiation significantly reduced locoregional relapse among DTC-positive patients compared with DTC-negative patients (interaction test: hazard ratio, 0.3; 95% confidence interval, 0.1-0.9; P=.02). IMN/SCN was the only irradiation volume with an impact on locoregional relapse in patients according to DTC status, and the predictive value of DTC status for the benefit of locoregional irradiation was independent of locoregional nodal status. This long-term analysis confirms the predictive impact of DTC status on the efficacy of regional radiation therapy for locoregional relapse in early breast cancer. After further studies, DTC status could be used as a decision tool to better tailor adjuvant radiation therapy in patients with early stage breast cancer.