Clinical Implication of Subcategorizing T2 Category in Metaplastic Breast Cancer.

Purpose: In the tumor, node, metastasis staging system for metaplastic breast cancer (MBC), the T2 category, encompassing a border spectrum of tumor sizes than T1 category, curiously lacks subcategorization.

Methods: Using the Surveillance, Epidemiology, and End Results database, data of 767 women diagnosed as T2N0-2 MBC between 2004 and 2016 were analyzed. The optimal tumor size cutoff was determined using X-tile software to facilitate the subclassification of T2 tumors. A comparison of breast cancer-special survival (BCSS) was conducted across three subcategories, with a median follow-up duration of 44 months.

Results: Of 767 patients, 136 (17.7%) died. Based on Kaplan-Meier analysis, 30 mm and 40 mm were selected as the cutoff values. Ten-year BCSS rate was 90.2% in patients with breast tumors ≤ 30 mm (T2a), 80.2% in patients with breast tumors ≤ 40 mm (T2b), and 68.2% in patients with breast tumors ≤ 50 mm (T2c) (log-rank p = 0.001). T2b (p = 0.009) and T2c (p < 0.001) subcategory showed worse BCSS than T2a subcategory. By multivariate analysis, T2b (T2a as reference, hazard ratio [HR], 1.610, p = 0.020) and T2c (HR, 1.981, p = 0.002) subcategory were significant independent prognostic factors of BCSS. By subgroup multivariate analysis, patients receiving breast-conserving surgery (BCS) plus radiotherapy (RT) had a better prognosis than that receiving total mastectomy (TM) in T2a stage. However, the prognosis was worse in BCS + RT group than TM group in T2c stage, while there was no difference between two groups in T2b stage.

Conclusion: Further stratification within the T2 category could enhance the precision of prognostic predictions and facilitate the customization of adjuvant treatments.