breast biopsy

My mom had a irregular mammogram. Then they asked for another mammograM and ultra sound. Yesterday I took her to the doctor to get her results. He said he had to touch her breast and see if he could feel the lump. He said he couldn't feel it. But the report said she had a spot or shadow show in the retort they gave her. He then said he wants to get a biopsy. What does that mean. I know what the procedure is. But is there a high chance of her having cancer. Couldn't they just tell if the spot was a cyst or something in the ultra sound. What does that spot mean even if there no lump. I'm really worried

Thanks for your response, I am just really worried. So good was a shadow to on the mammogram. She doesn't have a lump. Or so the doctor said he couldn't find it.