Possible Lobular, large suspicious area

Nothing showed up wrong with my 2001 mammogram.  This year, one year and 18 days later, after my mammogram, I was called back for an ultra sound.  The ultrasound showed a large ( 6 cm) suspicious area on left breast>  It is not on my arm side,but to the right of the nipple .  
It has undefined borders and can be felt as a firm area . I saw a surgeon last week.  The doctor pathologist at a large hospital where I took the ultrasound,  the surgeon, and my internist physician all agree that I need a biopsy, which has been scheduled for Friday, April 5.
Doctor,  this breast has no pain.  I had not noticed anything wrong before the ultrasound.  This breast has always been larger than my other one, (but both are large) and also has never had a standing nipple.  
I guess I am hoping they are wrong. They do say that there is a small chance that it could be  sclerosing adenosis.
I am going to have the biopsy (not a needle or core, but a peice of flesh). but doctor, I would like to know more about all this.   How could the spot have gotten so large so quick?  Does this mean that it is a fast growing type of cancer? And please discuss Scleosing Adenosis,  and Lobular Carcinoma.  

[CCF-RN,MSN-rf]

Dear Seven:  Sclerosing adenosis is a relatively benign breast lesion with no known predisposition for malignancy.  The average age of patients with sclerosing adenosis is 30.  Both mammographically and pathologically it can have characteristics that resemble carcinoma.  Biopsy is the standard approach.  Lobular carcinoma sends individual cells in little fingerlike projections - so it may feel more like a thickening than a lump.  A biopsy would be the correct procedure to determine the source of this finding.  Little can be said about it's size because we do not yet know what it is.