Dear Editor,

I want to congratulate Kubo et al. [1] for their article in which they studied the effects of adjuvant chemotherapy and/or trastuzumab and survival outcomes among 2736 patients with small (≤ 2 cm), node-negative, human epidermal growth factor receptor 2 (HER2)-positive breast cancer, using data from the population-based Japanese National Clinical Database (NCD). NCD data revealed that systemic treatment improved OS in pT1b, and pT1c, but not in pT1a node-negative HER2+ breast cancer patients. Multifocal (MF) and multicentric (MC) breast cancers are relatively common clinical entities ranging from 6 to 60%. TNM-staging guidelines have been used to stage MF and MC patients according to the diameter of the largest lesions, without taking other foci of disease into consideration [2]. Furthermore, we evaluated the prognostic performance of determining the T stage according to the total size of lesions compared with the size of the largest lesion in the breast in patients with MF/MC breast cancer. The T stage of MF/MC tumors was determined according to the largest lesion size (Tmax) as well as the sum of the longest diameters of the lesions (Tsum) in the breast. MF/MC tumors were identified in 323 of 3890 patients (8.3%) with breast cancer. After the T stage was reassessed using Tsum, it was observed that the DFS of the 32 patients with MF/MC tumors whose T stage advanced from stage I to II was closer to patients with stage II tumors ,compared with those with stage I [3]. Considering pT1a MF or MC cases, one would expect that these cases would be staged up to pT1b or pT1c if multiple foci sum up. This issue should be clarified by authors to define robust benefit of treatment in pT1a cases.