Background: Although post-mastectomy radiation therapy (PMRT) has shown benefits, its effects in patient subpopulations remain uncertain. Therefore, we assessed whether breast cancer subtype and p53 overexpression were associated with outcome after modified radical mastectomy (MRM), with or without PMRT.
Methods: We retrospectively analyzed the records of patients who underwent MRM, with or without PMRT, between January 1991 and December 2008. Patients were considered eligible if they had T3 or T4 stage disease; any T stage with N2 or N3 stage; any T or N stage with positive, close (<1 mm) resection margins; or skin, nipple, or pectoral muscle invasion. We used immunohistochemistry and/or fluorescent in situ hybridization to determine breast cancer subtypes and p53 overexpression status.
Results: We found that 104 patients were eligible, including 59 (56.7%) who underwent PMRT and 45 (43.3%) who did not. Median follow-up duration was 61.3 months (range 16.1-232.7). Overall survival (OS) was significantly longer in patients who underwent PMRT (P = 0.029). This trend was evident in the subgroup of luminal type A breast cancer (P = 0.017) and non-p53 overexpression (P = 0.026) patients. However, there was no significant survival benefit from PMRT in the subgroup of triple negative (TN) breast cancer (P = 0.528) and p53 overexpression (P = 0.189) patients.
Conclusions: The benefit of PMRT differed among subgroups with different breast cancer subtype and p53 overexpression. More efficacious systemic treatment strategies are needed, especially in patients at high risk for distant metastasis, to obtain optimal therapeutic gain.