In many developed countries, breast cancer is the commonest malignancy of women. The reduction in mortality due to breast cancer is believed to be attributable to detection of breast cancer at a very early stage. Most breast cancers of very early stage are non-palpable. It is usually necessary to obtain the tissue of the lesions in order to make a diagnosis in the case of suspicious non-palpable breast lesions. Either open biopsy using a hook wire or stereotactic core needle biopsy with a prone-type stereotactic mammography unit was used to obtain the tissue of non-palpable lesions until the vacuum-assisted biopsy device became available.