Invasive lobular carcinoma is a type of breast cancer that begins in the milk-producing glands (lobules) of the breast. Invasive lobular carcinoma is invasive cancer. That means the cancer cells have broken out of the lobule where they began and have the potential to spread to other areas of the body.
Invasive lobular carcinoma makes up a small portion of all breast cancers. The most common type of breast cancer begins in the breast ducts (ductal carcinoma).
Invasive lobular carcinoma typically doesn't form a lump, as most women expect with breast cancer. Instead, invasive lobular carcinoma more often causes a thickening of the tissue or fullness in one part of the breast.