We read with interest the article by Orsaria et al 1 on chromosome 17 ‘polysomy’ in invasive breast carcinoma, and its correlation with histological parameters and HER2 gene amplification. Although the authors mentioned briefly that ‘a simple increase of CEP17 copy number does not necessarily represent the presence of multiple copies of chromosome 17’ and that ‘focal pericentromeric gain or partial polysomy has been shown to exist in a majority of the so-called polysomy 17 cases’, they consistently use the term ‘polysomy 17’ throughout their manuscript, whereas, their definition of polysomy is based on the presence of ≥3 …