I am surprised you did not ask your doctor about this. He is the one who has all the information. As his patient you have the right to be fully informed.
Hi,
Well,with so little information you have provided regarding your Mammogram results,I can only presume that your Surgeon wants to remove the entire area of concern,because a biopsy could only sample some parts of the lump.Since you state that it's a very large hard mass,then the best thing to do is to have it completely removed,like your Surgeon suggested, so the pathologist can examine the cells of the entire lump to make sure that nothing abnormal is present.
Wishing you all the best and Benign findings!