Morphological and biomolecular characteristics of subcentimetric

Little information from clinical trials is available regarding the efficacy of trastuzumab treatment in subcentimetric breast carcinomas (BCs). The aim of this study was to verify the existence of correlations between HER2 and hormone receptor status, Ki67 values, grade, histotype and node involvement in a cohort of pT1a,b BCs from an area not widely covered by screening campaigns. A total of 410 pT1a,b BC formalin‐fixed paraffin‐embedded samples collected from eight Sicilian Anatomo‐Pathological Units (APUs) were classified according to the WHO classification and tumour grading was established. Estrogen and progesterone receptor status, Ki67 labelling index and HER2 status were available. Relationships between immunohistochemical data and clinicopathological characteristics were investigated using the Chi‐square test; the cohort was analysed with respect to pT1a and pT1b BC as well as to node status. Ductal infiltrating carcinoma was the prevalent histotype in the pT1a and pT1b stages; G2 was a more common tumour grade, with a range between 64.6% and 70% of pT1a and pT1b, respectively. Taking into consideration the lymph node involvement of pT1a,b BC, only 17.1% cases were node‐positive without a relevant difference between pT1a and pT1b. No significant differences between pT1a and pT1b BC cases emerged in relation to Ki67 LI, hormone receptors and HER2 status. T1a,b BC cases were stratified by node involvement and a significant relationship was observed with grade as well as with HER2 status. A significant relationship for pT1a cases emerged only for tumour grade, while pT1b cases showed a significant correlation exclusively with HER2 status. Our data clearly support the operative guidelines of the National Comprehensive Cancer Network. Therefore, the combined treatment with trastuzumab plus chemotherapy should be administered only to patients with pT1b or larger BCs. In small HER2‐positive pT1a or microinvasive BC, this therapy should be considered on a case‐by‐case basis, considering tumour grade as the first characteristic.