I had wondered that myself.
My initial core needle biopsy results came back as Atypical Ductal Hyperplasia. After having that biopsy, it seemed like the mass had changed a bit and become swollen, but that could have been me being paranoid.
I had my Lumpectomy about 3 months later and the whole mass was biopsied. It came back as an extremely rare Invasive Metaplastic Carcinoma AND also intermediate level DCIS.
I am not sure if the biopsy could have made a difference but definitely a great question to ask your doctor!
That being said, I do feel biopsies are an extremely important part of the process so that docs can learn pertinent information and come up with the best treatment plan for us to have.