Comparative Dosimetric Study of 3D Conformal Radiotherapy versus Volumetric Modulated Arc Radiotherapy in Synchronous Bilateral Breast Cancer

Abstract

Materials/Methods: From 2004-2013 patients with non-metastatic IBC who underwent breast conservation surgery (BCS) were identified from the NCDB. Patients' demographic, clinical, and treatment characteristics were collected and compared. Tumor (T) upstaging was defined by higher pathologic compared to preoperative stage. Nodal (N) upstaging was defined by clinically negative nodal (N) stage, but pathologically positive N stage. Bivariate unadjusted chi-square tests and adjusted logistic regression models were used to identify the predictors of pathologic upstaging at the time of initial resection. Results: A total of 707,798 patients were identified with non-metastatic invasive breast tumors who underwent BCS. Node upstaging data was available for 426,411 and tumor upstaging data for 490,142 patients. Pathologic T-and N-upstaging occurred in 5.8% and 13.1% of patients, respectively. On multivariable analysis, factors contributing to T-upstaging included: lobular or mixed histology, and higher grade (Table 1). Comparing tumor grade, T-stage upgrading occurred in 3.6%, 6.1%, and 7.6% and N-upstaging occurred in 9.4%, 14.4%, and 15.6% in grades 1, 2, and 3, respectively (p<.001, p<.001). On multivariable analysis, increasing grade remained significant to predict for N-upstaging (grade 3 vs 1, OR 2.06 (95% CI: 1.85-2.29). Estrogen (ER) and progesterone (PR) positive status was also significant for nodal, but not tumor, upstaging on multivariable analysis (ER pos, OR 1.14 (95% CI: 1.03-1.26); PR pos OR, 1.27 (95% CI: 1.17-1.38)). Conclusion: Using a modern American cohort, this NCDB analysis demonstrates patients with non-metastatic, IBC have a 5.8% risk of T-stage and 13% risk of N-stage surgical upstaging at time of initial resection. Lobular histology and higher grade tumor confer a higher risk of tumor upstaging, with grade 3 tumor doubling risk of T and N upstaging compared to grade 1. Receptor status has significant impact on nodal, but not tumor, upstaging. Patients should have appropriate pre-operative counseling regarding risk of tumor and nodal upstaging, particularly for higher grade IBC.