A very early type of breast cancer that develops within the milk-producing glands of the breast and does not penetrate through the walls of the lobules. Researchers think that lobular carcinoma in situ cells almost never progress to invasive lobular cancer. However, having this type of cancer places a woman at increased risk of developing an invasive breast cancer later in life which can occur in either breast. For this reason, it's important for women with lobular carcinoma in situ to have a physical examination three times a year and an annual mammogram.