Breast cancer happens when cells in the breast begin to grow out of control and can then invade nearby tissues or spread throughout the body. Large collections of this out of control tissue are called tumors. However, some tumors are not really cancer because they cannot spread or threaten someone's life. These are called benign tumors. The tumors that can spread throughout the body or invade nearby tissues are considered cancer and are called malignant tumors. Theoretically, any of the types of tissue in the breast can form a cancer, but usually it comes from either the ducts or the glands. Because it may take months to years for a tumor to get large enough to feel in the breast, we screen for tumors with mammograms, which can sometimes see disease before we can feel it.
How is breast cancer diagnosed and staged?
Once a patient has symptoms suggestive of a breast cancer or an abnormal screening mammogram, they will usually be referred for a diagnostic mammogram. A diagnostic mammogram is another set of x-rays; however, it is more complete with close ups on the suspicious areas. Sometimes, particularly if your doctors think that you may have a cyst or you are young and have dense breasts, you may be referred for an ultrasound. An ultrasound uses high-frequency sound waves to outline the suspicious areas of the breast. It is painless and can often distinguish between benign and malignant lesions.
Depending on the results of the mammograms and/or ultrasounds, your doctors may recommend that you get a biopsy. A biopsy is the only way to know for sure if you have cancer, because it allows your doctors to get cells that can be examined under a microscope. There are different types of biopsies; they differ on how much tissue is removed. Some biopsies use a very fine needle, while others use thicker needles or even require a small surgical procedure to remove more tissue. Your team of doctors will decide which type of biopsy you need depending on your particular breast mass.
Once the tissue is removed, a doctor known as a pathologist will review the specimen. The pathologist can tell if it is cancer or not; and if it is cancerous, then the pathologist will characterize it by what type of tissue it arose from, how abnormal it looks (known as the grade), whether or not it is invading surrounding tissues, and if the entire lump was excised, the pathologist can tell if there are any cancer cells left at the borders (also known as the margins). The pathologist will also test the cancer cells for the presence of estrogen and progesterone receptors as well as a receptor known as HER-2/neu.
The presence of estrogen and progesterone receptors is important because cancers that have those receptors can be treated with hormonal therapies. HER-2/neu expression may also help predict outcome. There are also some therapies directed specifically at tumors dependent on the presence of HER-2/nue.
In order to guide treatment and offer some insight into prognosis, breast cancer is staged into five different groups. This staging is done in a limited fashion before surgery taking into account the size of the tumor on mammogram and any evidence of spread to other organs that are picked up with other imaging modalities; and it is done definitively after a surgical procedure that removes lymph nodes and allows a pathologist to examine them for signs of cancer. The staging system is somewhat complex, but here is a simplified version of it:
Stage 0 (called carcinoma in situ)
Lobular carcinoma in situ (LCIS) refers to abnormal cells lining a gland in the breast. This is a risk factor for the future development of cancer, but this is not felt to represent a cancer itself.
Ductal carcinoma in situ (DCIS) refers to abnormal cells lining a duct. Women with DCIS have an increased risk of getting invasive breast cancer in that breast. Treatment options are similar to patients with Stage I breast cancers.
Early stage breast cancer where the tumor is less that 2 cm across and hasn't spread beyond the breast.
Early stage breast cancer where the tumor is either less than 2 cm across and has spread to the lymph nodes under the arm; or the tumor is between 2 and 5 cm (with or without spread to the lymph nodes under the arm); or the tumor is greater than 5 cm and hasn't spread outside the breast.
Locally advanced breast cancer where the tumor is greater than 5 cm across and has spread to the lymph nodes under the arm; or the cancer is extensive in the underarm lymph nodes; or the cancer has spread to lymph nodes near the breastbone or to other tissues near the breast.
Metastatic breast cancer where the cancer has spread outside the breast to other organs in the body.
Depending on the stage of your cancer, your doctor may want additional tests to see if you have metastatic disease. If you have a stage III cancer, you will probably get a chest x-ray, CT scan and bone scan to look for metastases. Each patient is an individual and your doctors will decide what is necessary to adequately stage your cancer.