A breast cancer diagnosis can be scary. A lot of things are likely to happen in rapid succession once a diagnosis is made.

For example, soon after a diagnosis is made, your doctor will want to conduct several tests to learn more information about the type of breast cancer you have. They’ll also test to determine the cancer’s size and whether it has spread to nearby lymph nodes or other organs and tissues.

This information will help your doctor determine the cancer’s stage. The stage of a cancerous tumor can tell doctors how advanced the cancer is. It can also tell your care team how the cancer might respond to treatment — and even how quickly it may be growing.

Other tests doctors use to determine treatment options include:

  • biomarkers that indicate whether the cancer is resistant to treatment or more likely to respond to treatment
  • hormone receptor and HER2 status which provides information about the effectiveness of hormone therapy
  • gene expression tests can help doctors make decisions about treatment following breast surgery

If you’re trying to understand what tumor size has to do with breast cancer staging, keep reading. In this article, you can read about breast cancer tumor sizes, as well as how tumor sizes affect treatment and growth rate.

Finding a breast cancer’s stage is a multi-step process. The tumor’s size and location help healthcare professionals determine the cancer’s stage. Other factors are considered, too.

Tumor stage

Healthcare professionals use the TNM System to understand a tumor’s stage.

  • T = tumor This tells you the size and location of the tumor.
  • N = lymph nodes This tells you if the cancer has spread to any lymph nodes and how many are affected.
  • M = metastasis This indicates the cancer has spread to other parts of the body.

Tumor size

Breast cancer tumors are divided into five categories based on size:

  • T0: This size of tumor is considered noninvasive. It’s very small and hasn’t spread.
  • T1: This tumor is less than 2 centimeters (3/4 inch). It may or may not have spread to nearby lymph nodes.
  • T2: This tumor is slightly larger, between 2 and 5 centimeters. Some stage 2 tumors are larger but haven’t spread to the lymph nodes. Others may be small but have spread to nearby lymph nodes.
  • T3: Tumor is greater than 5 cm.
  • T4: Tumor of any size with invasion into the chest wall or skin.

It’s important for your doctor and entire healthcare team to know the cancer’s stage in order to plan treatment. Treatment for breast cancer takes into account the tumor’s size, location, and spread, if there is any.

For example, cancers that are considered early stage may be treated with localized treatments, like surgery and radiation. This cancer may have a better prognosis.

For advanced-stage cancers, a doctor may use systemic treatments. These include chemotherapy, hormone therapy, targeted therapy, and more. Radiation may also be used for advanced-stage cancer, but other treatments will likely be used in conjunction.

Breast cancer cells are mutated cells — they don’t grow the way healthy cells do. Instead, they grow at different rates than other cells in the body. Different types of cancers also grow at different rates. That makes predicting how quickly a breast cancer tumor will grow difficult.

Most breast cancer tumors have been growing for several years before they’re found. The cells will need to divide as many as 30 times before the tumor is detectable. With each division taking 1 to 2 months, a tumor could be growing 2 to 5 years before it’s found.

But there are things a healthcare professional can do to determine if the cancerous tumor is growing quickly. Some tumor gradings will include information that indicates how likely the tumor is to grow and spread.

This information is usually gathered with a biopsy. In this medical procedure, a professional will remove a tissue sample from the affected area. That tissue will be sent to a lab where a specialist will review it.

Cancerous cells that are highly aggressive will look very different from normal, healthy cells. The greater the difference between the two types of cells, the higher the chances the cancer is aggressive. But cancer cells that look more like the other cells may be less aggressive.

If the biopsy suggests the cancer is likely to spread, you’ll be monitored closely for metastases. Cancer cells can spread via the lymph system, bloodstream, or directly into nearby tissues and organs.

Breast cancer can grow for years without a noticeable lump or bump in your breast tissue. A regular mammogram may detect the tumor before you can manually.

The earlier a breast cancer tumor is caught, the better the chances of a positive outcome. Treatments are typically more successful with early-stage cancers. If you can find the cancer before it has spread, you can reduce your risk of advanced cancer and metastases.