Although breast cancer has been surpassed by lung cancer as the leading cause of cancer deaths among American women, breast cancer remains the leading cause of non-preventable cancer deaths. There is an average risk of developing breast cancer of approximately 1 in 9 for a woman by the age of 85.
Breast cancer is not a single disease process. It has numerous variations. Furthermore, the outcome for an individual is determined not only by the cancer, but by the individual's response to the carcinoma (cancer).
Most breast cancers, about 90%, arise in the ducts. The earliest manifestation is "ductal carcinoma in situ", or DCIS. It is confined to the duct (therefore non-invasive), and can first appear as extremely tiny specks or calcifications on a mammogram. Though the exact numbers are not certain, it is felt that DCIS will progress to invasive cancer in at least 30 to 50% of women.
The only way that breast cancer can kill is though metastasis (spread outside of the breast). It becomes lethal when it gains the capability of breaking out of the duct and invading the surrounding tissue, gaining access to blood and lymphatic systems through which it can spread to other organs and destroy their function. But even invasive breast cancer can be successfully treated, if caught early enough on mammography or by breast exam. Invasive ductal carcinoma can appear as a lump, nodule, ill-defined density, or distortion on mammography, with or without calcifications.
Another less common variety of breast cancer is lobular cancer. These make up less than 10% of all breast cancers. They begin in the lining of breast lobules (glands) that are located at the ends of ducts. Invasive lobular breast cancer is as threatening as invasive duct cancer, but unfortunately it grows in a way that very often does not show up on a mammogram or a breast ultrasound. This is one reason why worrisome findings on breast self-exams or physical exams should not be ignored, in spite of a normal mammogram.
Lobular carcinoma in situ or LCIS is generally not felt to be a pre-invasive cancer. Rather, it is a significant indicator of increased risk for the development of invasive ductal or lobular cancer that can occur in the same or opposite breast. It is usually found incidentally, not because of a physical finding or finding on mammography.