PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s): The benefit of PMRT in women with pathologically proven T3N0M0 breast cancer remains controversial. Prior retrospective and subset analyses of prospective studies analyzing PMRT have shown conflicting results, particularly with respect to an improvement in overall survival (OS). SEER recently made information on chemotherapy (CT) available in patients diagnosed after 2004. Prior SEER analyses have shown an OS benefit with PMRT in the T3N0 patient population, however, this was not in association with chemotherapy. The aim of this analysis is to better understand the value of post-mastectomy radiation therapy in combination with CT in this select group of patients with respect to OS.
Materials/Methods: The SEER 18 registries database (November 2016 version) was queried to identify patients 18 and older with pathologically confirmed invasive ductal carcinoma and/or invasive lobular carcinoma diagnosed from 2004-2014 who underwent radical or modified radical mastectomy. Patients were excluded if they received neo-adjuvant radiation therapy or if the sequence of radiation therapy with respect to surgery was unknown. The relationship between PMRT and OS was determined using Kaplan and Meier survival curves that were subsequently compared using log rank analysis. Multivariable analysis (MVA) was performed using logistic regression analysis.
Results: A total of 1,901 patients met study criteria and 867 (46%) were identified who received PMRT and 1,034 (54%) who did not. The majority (77%) had invasive ductal cancer and the median age of the patients included was 57 years (range 22-97). 60% (n=1,142) of patients were ER+ and 62% (n=1,173) of patients received CT. The 5 and 10 year OS rates were significantly better with PMRT at 86% and 74%, respectively, compared to 74% and 56%, respectively, without PMRT (p<0.0001). In patients who received chemotherapy, the 5 and 10 year OS rates were 80% and 68% without PMRT, respectively, compared to 88% and 77% with PMRT (p=0.0006). In the subset of patients who were not known to have received CT, 5 and 10 year rates of overall survival were 69% and 47% respectively in patients who did not receive PMRT compared to 77% and 60% in patients who did (p=0.047). For patients who were ER+, 10 year OS was found to be 79% in patients who received PMRT compared to 52% in those who did not (p<0.0001). 10 year OS was 68% in ER- patients who received PMRT compared to 62% in those who did not (p=0.023). On MVA, the use of PMRT remained significant (OR 0.64, 95% CI: 0.50-0.83).
Conclusion: PMRT improved overall survival in patients with pathologically proven T3N0 breast cancer following radical or modified radical mastectomy both on univariate analysis and MVA. This survival benefit of PMRT extends to women who are ER+ or ER- as well as those who have received chemotherapy.
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