My mum is going through this at the moment - she had a routine mammogram which picked up calcification in her breast tissue. She had more tests and a biopsy, and in her case they have picked up pre-cancerous cells and she needs surgery to remove a small amount of tissue.
Here's what the NHS Direct site says...
"However, if you have calcification, it does not mean that you have cancer, and you will need further tests to confirm a diagnosis."
So it maybe something, it may be nothing, but needs to be checked out.