Dear Editor,

We read with great interest the article by Rask et al. [1] which analyzed the long-term results of small breast carcinomas (BC) according to molecular subtypes. Tissue samples from 445 women with node-negative BC ≤ 15 mm, treated in 1986–2004, were classified into surrogate molecular subtypes. They concluded that stage 1 TNBC or Luminal B-like (HER2-) tumors behave more aggressively and women with HER2 + /ER + tumors do not have an increased risk of distant metastasis or death, absent targeted treatment. Authors described the small tumors if tumor size is ≤ 15 mm. However, definition of small breas tumors are not strictly described in the literature. Furthermore, one study defined small tumors if tumor size is ≤ 10 mm (T1a, T1b) [2]. These descriptions are not concordant with TNM classification of the AJCC Breast Cancer Staging System. According to this guideline, small tumors are considered as all T1mi, a, b, c tumors. T1mi is a tumor that is 1 mm or smaller. T1a is a tumor that is larger than 1 mm but 5 mm or smaller. T1b is a tumor larger than 5 mm but 10 mm or smaller. T1c is a tumor larger than 10 mm but 20 mm or smaller [3]. In conlusion, the current study categorized ≤ 15 mm tumors as small tumors in their study. Their conclusion would not represent the outcome of all small tumors as described in TNM classification of the AJCC Breast Cancer Staging System. This issue merits further investigation.