Breast cancer is classified into different stages based on the tumor’s size and whether cancer cells have spread to other parts of the body. Determining your cancer’s stage through a mammogram and other imaging techniques can help your doctor determine your prognosis and the best treatment options.
Oncologists classify breast cancer from stage 1 to stage 4 (also referred to as stage I to stage IV). Cancer specialists determine this classification by using the TNM (tumor, node, and metastasis) system, which stages tumors based on:
Each letter is assigned a number, often with a letter following it. A lower number corresponds to early-stage, localized breast cancer, and a higher number indicates more advanced, metastatic breast cancer.
Other information is also used to better understand the stage of the cancer. These details may include:
Following a breast cancer diagnosis, a doctor will determine the most effective treatment based on the cancer’s stage.
Invasive breast cancer occurs when cancer cells have started to move from their original location — usually in the milk ducts — into the surrounding breast tissue. Stage 1 breast cancer is the earliest form of invasive breast cancer. It may further be classified into substages: stage 1A and stage 1B.
Stage 1A breast cancer is characterized by a breast tumor measuring up to 2 centimeters with no cancer cells found outside the breast.
Stage 1B breast cancer can signify one of two possibilities:
Treatment options for stage 1 breast cancer typically include surgery to remove the affected tissue. Radiation and drug therapy may be used as adjuvant therapy — therapy used after surgery — to lower the chance of recurrence.
Mastectomy and lumpectomy (also called breast-conserving surgery or partial mastectomy) are the two options for surgical treatment of stage 1 breast cancer.
A mastectomy is a surgical procedure that removes all breast tissue. Different types of mastectomies may be performed depending on how aggressive the cancer is. Stage 1 breast cancer is likely to be treated with a total mastectomy, which removes the breast but leaves nearby lymph nodes. A mastectomy is necessary for people with large breast tumors. Some people may choose to have reconstructive surgery following a mastectomy to restore the appearance of their breast or breasts.
An alternative to mastectomy is a lumpectomy. In this procedure, a surgeon removes the breast tumor and some of the surrounding tissue. This breast-conserving surgery is often the preferred option for people with small tumors that are more easily removed. Following lumpectomy, radiation therapy is commonly used to kill any remaining cancer cells that may have been missed.
Several studies have shown that a lumpectomy plus radiation leads to similar or even better rates of survival than mastectomy for early stage breast cancer. Ultimately, the type of surgery chosen should be based on both the stage of the cancer and the preference of the person undergoing the surgery.
If the cancer cells have spread into the lymph nodes, such as in stage 1B cancer, a lymph node dissection (or biopsy) is generally needed to remove the affected tissue. An axillary lymph node biopsy to remove underarm lymph nodes that contain cancer cells may be performed after surgery.
A less invasive procedure, sentinel lymph node biopsy, can remove affected lymph nodes — and possibly eliminate the need for surgery. In some cases, axillary lymph node biopsy may still be required.
Chemotherapy is a common oncology treatment that selectively eliminates breast cancer cells. Although chemotherapy is typically used to kill tumor cells left behind after surgery, it can be used to shrink the tumor before surgery in more advanced cases.
To consider hormonal therapies, a doctor will confirm the hormone receptor status of the cancer. Some breast cancers are positive for the estrogen receptor or progesterone receptor. These hormone receptors are proteins that play a role in breast cancer growth.
People with hormone receptor-positive breast cancer in stage 1 are typically eligible for treatment with tamoxifen or exemestane (Aromasin), though exemestane is considered only for those who are postmenopausal. These hormonal therapy drugs specifically target the hormone receptors and may lower the likelihood of cancer recurrence (returning after treatment).
Targeted therapy works by stopping the function of a particular protein or group of proteins. HER2, a protein present at high levels in some breast cancers, affects how the cancer grows. HER2-positive stage 1 cancers may be treated with drugs that specifically target this protein.
Breast cancer that is negative for estrogen receptors, progesterone receptors, and HER2 receptors is called triple-negative breast cancer. This type of breast cancer is particularly difficult to treat. Immunotherapy may be recommended as an additional treatment option. Immunotherapy drugs interact with a person’s immune system so that it can recognize and fight the cancer cells.
Survival rates for breast cancer are determined based on whether the cancer is localized (occurs only in the breast), regional (has spread to nearby tissues), or distant (has spread throughout the body).
Stage 1 breast cancer is localized and has a very favorable prognosis (outlook), with a five-year survival rate of at least 99 percent. Early diagnosis helps, as does thorough tumor testing, to ensure that each person receives the right cancer care.
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