Depends. There several types. Fine needle (fna), small and large bore core needle biopsies. Fna is the least invasive and equivalent to cores but only if done by an expert trained in this technique. As that skill is rare in the us, cores are much more common. Small cores are usually done under local for masses while large cores are used for mammographically detected lesions, also under local.
Biopsy. Try this website for a description: http://ww5.komen. Org/BreastCancer/CoreNeedleBiopsy. Html.