TNM Classification: Staging is a way to classify how large a cancer has grown and how far it has spread at the time of diagnosis. Knowing the stage of the cancer helps determine the best treatment for the cancer. Cancer doctors use the “TNM” staging system to classify a patient’s stage of cancer. “T” stands for the tumor size, “N” stands for whether the lymph nodes in the region have cancer in them, and “M” stands for whether the cancer has spread (or metastasized) from the breast to other parts of the body such as the liver, lungs, bones. The T, N, and M are then combined and form the stage of the cancer (from stage 0 to stage IV).
Clinical staging: When a patient is initially diagnosed with breast cancer (after the biopsy is performed but before surgery has been done), the doctor will assess the clinical stage, based on the physical exam and imaging findings. They will estimate the size of the mass in the breast and will assess for the presence of any abnormal lymph nodes by physical exam and imaging studies. Occasionally, scans of the body will be performed (such as a CT scan, bone scan, PET scan, chest x-ray, MRI or ultrasound of the abdomen). These imaging studies are usually not recommended unless the lymph nodes are felt to be abnormal on examination or the patient has signs or symptoms that the cancer has spread to other parts of the body.
Pathologic staging: At the time of surgery (for stage 0-III breast cancer), the surgeon will remove the breast tumor and (for stage I-III breast cancer) some of the regional lymph nodes. After surgery, a pathologist will examine all the tissue removed at the time of surgery and will generate a “pathological stage.” This stage is most accurate as the pathologist is able to give an accurate size of the actual tumor (which is sometimes different than the imaging or examination estimated prior to surgery) and will also give an accurate assessment of whether lymph nodes are involved by cancer.
Stage 0 breast cancer is ductal carcinoma in situ (DCIS), which is a pre-cancer that does not have the potential to spread elsewhere. It is considered to be curable by surgery. Often radiation is also offered, to reduce the risk of cancer returning in the same breast. Patients with stage 0 cancer are at higher risk of developing a new cancer in either breast compared to someone who never has had DCIS. For this reason, sometimes patients are treated with medicine (such as tamoxifen or an aromatase inhibitor) to reduce the risk of another breast cancer in either breast.
Stage I and II breast cancers are early stage, localized tumors. Stage I breast cancer is small (less than 2 cm) and has not spread to the lymph nodes. Stage II cancers are up to 5 cm and may have some lymph nodes involved by cancer. These tumors are generally treated with surgery and sometimes radiation to the breast and nearby lymph nodes. Patients will also receive systemic therapy. Those patients with hormone receptor positive tumors will generally be given endocrine therapy for at least 5 years. Patients with HER2 positive tumors will almost always be given HER2-targeted therapy plus chemotherapy. And patients without ER, PR, or HER2 expression (so called “triple negative” tumors) will be treated often with chemotherapy.
Stage III breast cancers are larger tumors (over 5 cm), often with spread to the lymph nodes. These tumors are still potentially curable, but are considered to be “locally advanced” and are generally treated aggressively with surgery, radiation therapy, chemotherapy and, if HER2-positive, HER2-targeted therapy.Stage IV (metastatic) breast cancer is breast cancer that has spread outside of the breast and lymph nodes and can be seen on an imaging scan in other organs such as the bone, brain, skin, liver, or lungs. (Note: When cancer has spread to a different organ, it is called metastatic breast cancer of that organ. It is not a new cancer in that organ. For example, when breast cancer has spread to the liver, it is not called “liver cancer,” it is called “metastatic breast cancer to the liver.”) Metastatic breast cancer is sometimes diagnosed in a woman who never has been diagnosed with breast cancer before. This is termed “de novo” metastatic breast cancer and occurs only ~10% of the time in the US. The majority of patients diagnosed with metastatic breast cancer have a prior history (months or years before) of early stage breast cancer. In either case, it is important for a patient to have a biopsy of the metastatic tumor seen on imaging studies to confirm that it is indeed breast cancer and to retest the tumor subtype (ER, PR and HER2 protein expression). Metastatic breast cancer is a chronic illness. It is not considered to be curable however it is highly treatable. Due in large part to significant advances made in the systemic treatment of breast cancer, patients can often live many years with metastatic disease. There are two main goals of treatment for patients with metastatic disease: (1) to control the disease with medicine and (2) to preserve (or improve) quality of life. There are numerous therapies available to women with metastatic breast cancer, and many innovative, targeted treatments are currently in late stage clinical trials that have the potential to improve long-term outcomes for women with metastatic disease.