As PJ said a tumor starts with just one cell that becomes mutated.  When I felt my lump it felt like a marble and measured 2x2x1.5 cm's when it was removed- that along with other factors put me at a Stage IIa Invasive Ducatal Carcinoma Breast Cancer.  I was just 31 with no history of cancer whatsoever. My other breast consisted of lots of lumpy breast tissue, but no cancer.

The size of tumors is most important when it comes to staging cancer.  I know this is venturing off topic just a bit - but according to my breast cancer bible (Breast Cancer for Dummies) there is a multitude of stages to cancer and they are based on the size of the tumor along with other pathology report test results.

Here's the breakdown, just for your information:

Stage 0 - includes 2 different types of cancer LCIS & DCIS, though neither have spread beyond where they started.

Stage 1 - tumor is 2cm or smaller and has not spread at all to lymph nodes or organs.

Stage 2A - tumor is 2cm or smaller, up to 1 node involved, but no metastasis.

Stage 2B - tumor is 2cm to 3cm, up to 1 node involved, but no metastasis.

Stage 3A - tumor is 0cm to 3cm, 1 or 2 nodes involved, but no metastasis.

Stage 3B - tumor is 4cm, up to 2 nodes involved, but no metastasis.

Stage 3C - tumor of any size, 3 or more nodes involved, but no metastasis.

Stage 4 - any size tumor, any number of nodes involved, and metastasis.

Before you start worrying about sizing and staging, first find out what the results of your mammogram will be on Monday.  As PJ suggested, you have fairly good odds of the lump being nothing even though your fammily has a history of cancer.

So good luck to you.  Please keep us posted on your outcome.

Angi