Stage 1 breast cancer is the earliest stage of invasive breast cancer. If treated, it has a positive outlook.

Regular breast cancer screening is an important factor in the detection of stage 1 breast cancer. Like most types of cancer, the earlier stage 1 breast cancer is detected and treated, the better the outcome will likely be.

Your diagnosis, type of breast cancer, and medical history are all factors that will determine what type of treatment plan your doctor will develop with you.

Read on to find out how stage 1 breast cancer is staged and what you can expect from treatment. Also included are some helpful resources for support and help as you navigate your breast cancer journey.

Stage 1 breast cancer is the earliest stage of breast cancer. Experts divide it into stages 1A and 1B, based on tumor size and spread to lymph nodes.

To understand how these subcategories are defined, it’s helpful to break down the TNM system of classification.

TNM classification

T measures tumor size:

  • TX. Nothing about the primary tumor is known, or its size cannot be measured.
  • T0. Primary tumor cannot be found.
  • Tis. Cancer cells are in their original location, or in situ.
  • T1 to T4. Tumor size from small to large.

N measures lymph node spread:

  • NX. No information on lymph nodes can be accessed.
  • N0. No cancer cells are found within nearby lymph nodes.
  • N1 to N3. Refers to the location, size, or number of nodes with cancer cells.

M measures metastasis or spread to other body parts:

  • M0. Cancer cells have not spread.
  • M1. Cancer cells have spread to distant sites.
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In stage 1 breast cancer
  • The tumor size is T0 or T1.
  • The lymph node spread is N0 or N1.
  • The metastasis is M0.

The reason for this classification is that the tumor remains small in stage 1. If there is any lymph node spread, it is microscopic.

Also, because the tumor is small and localized, there won’t be any metastasis, or spread to other parts of the body.

Stage 1 breast cancer is then further subdivided into stages 1A and 1B.

Stage 1AThe tumor is about 2 centimeters or smaller in size and has not spread outside the breast.
Stage 1BEither the tumor is smaller than 2 centimeters, or no tumor is found within the breast (less common). Small clusters of breast cancer cells no more than 2 millimeters in size are present in the lymph nodes.

Your doctor and healthcare team will consider many different factors before deciding on the best type of treatment for your stage 1 breast cancer. Besides knowing the TNM classification of your cancer, they will also test a sample of cancer cells for:

  • tumor grading
  • the presence of specific receptors

Knowing more about the tumor grade and the types of receptors that are on the surface of the cancer cells will be especially helpful in determining the right type of treatment for you.

Tumor grading gives an indication of how fast the cancer cells are likely to grow and spread beyond the breast. A higher grade is considered to be more aggressive.

How breast cancer cells are graded

  • G1. Cells are well differentiated — this is considered low grade.
  • G2. Cells are moderately differentiated — this is considered intermediate grade.
  • G3. Cells are poorly differentiated — this is considered high grade.
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Your healthcare team will also test the cancer cells for receptors that are located on the outside of the cells. Knowing which receptors are present can help determine what type of treatment is likely to be more effective.

Receptor status of breast cancer cells

Breast cancer cells are tested to determine whether they have any of the following receptors:

  • Estrogen receptors: estrogen receptor-positive (ER+) or estrogen receptor-negative (ER-) status
  • Progesterone receptors: progesterone receptor-positive (PR+) or progesterone receptor-negative (PR-) status
  • HER2 (a growth-promoting protein): human epidermal growth factor receptor 2-positive (HER2+) or human epidermal growth factor receptor 2-negative (HER2-) status
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The type of treatment that’s recommended for stage 1 breast cancer will depend on a variety of factors, such as:

  • the tumor size
  • lymph node involvement
  • the tumor grade
  • receptor status
  • gene mutations

Local treatment: surgery and radiation

If you receive a diagnosis of stage 1 breast cancer, your doctor may recommend local treatments such as surgery and radiation therapy to treat your breast cancer at the site.

Both lumpectomy and mastectomy are options for stage 1 breast cancer. Your doctor will help determine what is right for you based on the tumor size, grade, and level of spread.

  • Lumpectomy. Also known as breast-conserving surgery, a lumpectomy is the least invasive surgery for breast cancer. With this procedure, a surgeon will remove the tumor and some surrounding tissue, but will leave as much of your breast as possible so that it looks a lot like the original breast.
  • Mastectomy. A mastectomy involves the removal of the entire breast. There are different types of mastectomies. Some types of mastectomies involve the removal of the lymph nodes. Other types can preserve the breast skin or the nipple and areola, especially with early stage breast cancer.

Doctors typically recommend radiation therapy after a lumpectomy for stage 1 breast cancer treatment. Radiation therapy helps destroy any cancer cells that may have been left behind after the surgery. This helps lower the chance of the breast cancer coming back.

Radiation is less often needed after a mastectomy with stage 1 breast cancer.

Beyond local treatments, your doctor might recommend systemic treatments for stage 1 breast cancer.

Systemic treatments for stage 1 breast cancer

Systemic treatments, often termed add-on or adjuvant treatments, treat breast cancer throughout your body and not just at the site of the tumor.

These treatments help destroy cancer cells that have spread beyond your breast but are still too small to be spotted. They include the therapies outlined below.


Doctors may recommend chemotherapy, also called chemo, after surgery to help destroy any undetected cancer cells. Chemotherapy may also lower your risk of the cancer coming back at a later stage.

Chemotherapy may be recommended for a smaller tumor if:

  • Any cancer cells were found in the lymph nodes.
  • You score high on a gene test such as Oncotype DX, which shows whether chemotherapy could help treat your breast cancer and if it’s likely to come back after surgery.
  • The cancer cells are progesterone receptor- and estrogen receptor-negative.
  • The breast cancer cells are positive for human epidermal growth factor receptor 2 (HER2) — various therapies can target these receptors.

Hormone therapy

Hormone therapy can be used to help slow down the growth of cancer cells in people with estrogen receptor-positive (ER+) or progesterone receptor-positive (PR+) cancer cells. Hormone therapy works by blocking hormone receptors on the cancer cells or by lowering the amount of estrogen produced in your body.

Your doctor may prescribe tamoxifen if you’re still having your menstrual period. If you’ve reached menopause, they may prescribe an aromatase inhibitor such as anastrozole (Arimidex), letrozole (Femara), or exemestane (Aromasin).

You may also be prescribed a medication such as leuprolide (Lupron) or goserelin (Zoladex) to stop the production of estrogen. Or, you could opt to have your ovaries removed. This can prevent the production of hormones that fuel cancer growth.

It’s important to ask your doctor about the potential side effects of hormone therapy before you begin this treatment, so can you know what to expect.

Targeted therapy

Targeted therapies can be used to treat HER2-positive breast cancer. These targeted drugs can help block the HER2 proteins that the cancer cells need to grow.

Targeted therapies may also help boost the effects of chemotherapy. Examples of targeted therapy drugs include trastuzumab and pertuzumab.

Breast cancer terminology

To better understand breast cancer terminology and prepare for meeting with your doctor, check out these 58 words you should know about breast cancer.

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A 2020 review that was published in the Journal of Cancer Survivorship found that a long-term care plan was key to curbing the impact of cancer treatment and improving the overall wellness of cancer survivors.

But, according to a 2019 study, approximately 21 percent of breast cancer patients stop seeing their doctor for follow-up care within 5 years of being diagnosed with breast cancer.

To maximize your long-term health and wellness, it’s important to stick to the follow-up care plan that your doctor recommends for you. This will likely involve:

  • Doctor visits. These may occur every few months at first and then gradually scale down to once a year after 5 years.
  • Hormone therapy. You may take hormone therapy for 5 years or longer if you had estrogen receptor- or progesterone receptor-positive breast cancer.
  • Taking bone strengthening agents. These include treatments such as zoledronic acid (Zometa) or denosumab (Prolia) if you’re at increased risk of bone fractures or osteoporosis due to certain cancer treatments.
  • Breast imaging. If you had breast-conserving surgery or lumpectomy, you may need imaging 6 to 12 months after surgery and radiation treatment. You may have imaging at least once a year after that.
  • Pelvic exams. If you took hormonal drugs such as tamoxifen, these drugs can raise your risk of uterine cancer. Annual pelvic exams are also recommended even if you’re not taking tamoxifen.
  • Bone density tests. These tests are recommended if you took an aromatase inhibitor or went through menopause as a result of treatment.
  • Other tests. You may have imaging and blood tests, bone scans, or biopsies if you have symptoms or findings that suggest your breast cancer might have returned.

The outlook for stage 1 breast cancer is good. This is because it’s an early stage of breast cancer and hasn’t yet spread to the lymph nodes or to other parts of the body.

A 2018 study supports previous reports that show the 5-year survival rate among people with stage 1 breast cancer to be greater than 90 percent in most cases.

If you’ve received a diagnosis of breast cancer, you may be feeling fearful and anxious. But you are not alone. You may want to consider reaching out to a breast cancer support group or online community for help, advice, and resources.

Many other people are dealing with exactly the same questions and concerns that you are. And many people have also survived breast cancer and can provide invaluable advice and support.

You may want to:

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Stage 1 breast cancer is the first stage of invasive breast cancer. It’s characterized by a small tumor or microscopic spread to the lymph nodes. Understanding the classification of stage 1 breast cancer and what to expect from your treatment plan can help you feel more in control of your health.

The first line of treatment for stage 1 breast cancer often involves surgery followed by radiation. Your doctor can also add systemic therapy such as chemotherapy and hormone or targeted therapy to your care plan if they believe these treatments are necessary.

With 5-year survival rates above 90 percent, the outlook for stage 1 breast cancer is very positive. The earlier breast cancer is detected and treated, the better the outcomes tend to be.