For those of you that don't know, IDC is infiltrating ductal carcinoma, also known as invasive ductal carcinoma.  It's a type of breast cancer - the type I was diagnosed with 3 years ago.  What I have now is called a recurrence.

Here’s the low-down on IDC, it's atypical cells.....cells that, for an unknown reason, mutated as they grew,and collected in the ducts in your breast. Ducts are the tiny tubes that carry milk from the lobules, where it’s made, to the nipple. At some point, these atypical cells broke through the duct wall, and started moving into the surrounding tissue. This is when your cancer crossed the line from DCIS–ductal carcinoma in situ–to invasive (infiltrating) ductal carcinoma–IDC.

So you might wonder what suddenly made these cells move into the rest of my breast, rather than just continue to collect?

Researchers would love to know the answer: if they knew WHY cells suddenly start to move and migrate, they might be able to figure out how to stop them. But right now, their best guess is not that the cells themselves suddenly became more aggressive, but that that something around the cells–a hormone, other cells–gave them the “go ahead” to move. But that’s still a theory; research continues.

Infiltrating or invasive ductal carcinoma is the most common type of breast cancer; 70% of women with breast cancer have this diagnosis. And 80% of women with invasive breast cancer have IDC.

With odds like that, it's safe to say that IDC is one of the most common forms of breast cancer.