Predicting locoregional recurrence in triple-negative breast cancer using novel molecular subtyping.

Abstract

e12549 Background: Triple-negative breast cancer (TNBC) presents a poorer prognosis compared to other breast cancer subtypes, characterized by a higher likelihood of early recurrence and increased incidence of visceral metastases. Evidence from numerous randomized clinical trials indicates that postmastectomy radiotherapy (PMRT) reduces locoregional recurrence (LRR) and improves breast cancer survival in TNBC. Previous reports creatively divided TNBC into four molecular subtypes for personalized treatment. The present study aims to elucidate patterns of LRR in different subtypes of TNBC after PMRT. Methods: From 2019 to 2022, data from 349 AJCC 7th edition stage II-III breast cancer patients treated with mastectomy and PMRT were retrospectively analyzed. These patients were classified into the basal-like immune-suppressed (BLIS) and non-BLIS groups based on the immunohistochemistry biomarkers. The cumulative incidence function was applied to estimated LRR rates, with death as a competing risk, using Gray's test for comparisons. Results: According to the IHC results, a total of 255 patients belonged to the non-BLIS group and 94 to the BLIS group. The 3-year LRR for the entire cohort was 5.16%. There were 9 cases each in the non-BLIS subtype (3.5%) and BLIS subtype (9.6%). The cumulative incidence of LRR between the two groups was significantly different, with a rate of 4.0% in the non-BLIS group and 9.0% in the BLIS group ( P = 0.02). Among the 18 patients with LRR in the whole population, 11 had isolated LRR and 7 were diagnosed with LRR with concurrent distant metastases. The most common area of recurrence in both subtypes was the supraclavicular region. The majority of recurrences occurred within the RT field (in-field), and no isolated out-of-field relapse was observed. In multivariate analysis, independent factors predicting higher LRR were the BLIS subtype (HR = 3.06, P = 0.02). Conclusions: Study results suggest that TNBC of the BLIS subtype is at higher risk for LRR. Immunohistochemistry-based molecular typing may serve as a prognostic biomarker to guide postmastectomy radiotherapy in patients with TNBC. New strategies are needed to improve local control rates in patients with BLIS subtype.