A breast cancer diagnosis brings about a range of emotions. It also sparks many questions, including ones surrounding what your cancer's stage might mean for you.

"Breast cancer staging is a critical process that helps us determine the extent of the cancer — whether it's localized to breast tissue or has spread beyond it," says Dr. Hahn Mai, a breast medical oncologist at Houston Methodist. "This information is important for a number of reasons, namely because it helps plan treatment accordingly."

Knowing the stage of breast cancer also provides a roadmap for discussions with your doctor, helping you ask relevant questions and seek out appropriate support resources.

The positive news: Less than 3% of women diagnosed with new or recurrent breast cancer succumb to it.

How is breast cancer staged?

Staging entails a comprehensive evaluation of the cancer. The following key factors are analyzed:

• The size of the tumor
• Whether the cancer has spread to nearby lymph nodes
• Whether the cancer has spread to distant organs
• The tumor's molecular subtype (whether certain proteins — estrogen receptor, progesterone receptor and/or HER2 — are made by the cancer cells)
• The cancer's grade (how aggressive the cancer cells look under a microscope)

Several tests may be used to collect this information, such as a mammogram, ultrasound, breast biopsy, lymph node biopsy, PET scan and MRI scan. Not everyone will need all of these tests. Your care team will help you understand which are helpful for your specific situation.

Based on the results of these tests, your doctor will assign a stage, which can help as they talk to you about prognosis, treatment and more.

How many stages of breast cancer are there?

There are five stages of breast cancer. The earliest is stage 0, which is called carcinoma in situ. It's the only form of breast cancer that's considered non-invasive. The most advanced is stage IV, which is also called metastatic breast cancer.

The lower the number of a stage, the less the cancer has spread. The higher the number, the more it has spread — which generally also means that more aggressive treatment will be needed.

Which stages of breast cancer require a mastectomy?

Surgery is almost always needed to treat breast cancer. The exception is stage IV breast cancer, in which there's very rarely a role for surgery with metastatic disease.

"In particular, surgery is essential for early-stage breast cancer — stages I and II — because it can render a person free of disease," explains Dr. Mai.

Small, early-stage tumors can often be removed using a breast-conserving procedure called a lumpectomy, which removes the tumor and just a small amount of healthy breast tissue. The amount removed depends on the size of the tumor.

A mastectomy, on the other hand, is when the entire breast is removed. It may be used to treat stage 0 to stage III breast cancer. There are several reasons your doctor may recommend a mastectomy over a lumpectomy, even in cases of early-stage cancer.

"If a lumpectomy isn't feasible due to a tumor's large size or when cancer encompasses two or more quadrants of the breast, a mastectomy is required," explains Dr. Mai.

After a mastectomy, breast reconstruction can be used to rebuild your breast — using either an implant or your own tissue, typically from your belly. Newer techniques can also help spare the nipple and breast skin in some cases, improving the appearance after mastectomy and reconstruction.

(Related: Breast Reconstruction: 5 Things to Know If You Need Breast Cancer Surgery)

Which stages of breast cancer require chemo and radiation?

In addition to surgery, most stages of breast cancer either require or benefit from chemotherapy and/or radiation. The goal of these treatments is to kill cancer cells or stop them from growing within the breast tissue. Chemotherapy is delivered by medications, while radiation therapy uses high-energy beams.

These treatments may be used to help shrink the tumor before surgery or to kill any lingering cancer cells that may remain after surgery, helping ensure the cancer doesn't come back.

"If an early-stage cancer is aggressive, we may recommend chemotherapy," says Dr. Mai. "Whether chemotherapy or radiation is useful for the other stages of breast cancer depends on a few factors, such as the molecular subtype of the cancer and the type of breast surgery used to remove the tumor."

For instance, HER2-positive (HER2+) breast cancer often requires chemotherapy. So does triple-negative breast cancer, a less common but aggressive type that lacks the molecular features often targeted during breast cancer treatment: estrogen receptor, progesterone receptor and HER2.

"Radiation therapy is indicated when a patient undergoes a lumpectomy, though patients also need radiation therapy after mastectomy in certain cases," adds Dr. Mai.

For stage IV breast cancer, chemotherapy is used — if it can be tolerated — to help control spread and relieve symptoms. It's typically combined with other therapies, such as hormone therapy, targeted therapy and immunotherapy.

Is breast cancer stage related to how curable cancer is or its likelihood to recur?

Staging doesn't just help inform breast cancer treatment plans; it can also help provide a better understanding of prognosis. Outcomes are also based on other factors, however, such as the type of breast cancer.

"Stages 0 to III are potentially curable," says Dr. Mai. "By definition, stage IV breast cancer is not curable."

That said, newer treatments are helping people with metastatic breast cancer live longer. The average lifespan for people diagnosed with metastatic breast cancer can vary significantly and depends on factors such as the type of breast cancer, how it responds to treatment, the individual's overall health and other factors, like lifestyle.

Staging can also help gauge how likely it is for breast cancer to come back after treatment. As a general rule, the more advanced the stage, the more likely the tumor is to recur.

"Stage II and III patients have a higher likelihood of recurrence compared to those with stage 0 or I," says Dr. Mai. "Recurrence is also influenced by the type of breast cancer."

For instance, triple-negative breast cancer and inflammatory breast cancer are more likely to recur than other types.

Important to note is that treatment outcomes are also influenced by a patient's compliance with their care plan. While a diagnosis can't be changed, following your doctor's guidance can influence treatment outcomes and risk of recurrence.

That's key because when detected early, most breast cancers are curable. And while some patients do recur, most do very well during initial treatment.