When receiving treatment for breast cancer, women will learn about cancer staging. According to the nonprofit organization Breastcancer.org, determining the stage of the cancer helps patients and their doctors figure out the prognosis, develop a treatment plan and even decide if clinical trials are a valid option.

Typically expressed as a number on a scale of 0 through IV, breast cancer stage is determined after careful consideration of a host of factors. The staging system, sometimes referred to as the TNM system, is overseen by the American Joint Committee on Cancer and ensures that all instances of breast cancer are described in a uniform way. This helps to compare treatment results and gives doctors and patients a better understanding of breast cancer and the ways to treat it.

Breastcancer.org notes that the TNM system was updated in 2018, but before then was based on three clinical characteristics:

• T: the size of the tumor and whether or not it has grown into nearby tissue

• N: whether the cancer is present in the lymph nodes

• M: whether the cancer has metastasized, or spread to others parts of the body beyond the breast

While each of those factors is still considered when determining breast cancer stage, starting in 2018, the AJCC added additional characteristics to its staging guidelines, which make staging more complex but also more accurate.

• Tumor grade: This is a measurement of how much the cancer cells look like normal cells.

• Estrogen- and progesterone-receptor status: This indicates if the cancer cells have receptors for the hormones estrogen and progesterone. If cancer cells are deemed estrogen-receptor-positive, then they may receive signals from estrogen that promote their growth. Similarly, those deemed progesterone-receptor-positive may receive signals from progesterone that could promote their growth. Testing for hormone receptors, which roughly two out of three breast cancers are positive for, helps doctors determine if the cancer will respond to hormonal therapy or other treatments. Hormone-receptor-positive cancers may be treatable with medications that reduce hormone production or block hormones from supporting the growth and function of cancer cells.

• HER2 status: This helps doctors determine if the cancer cells are making too much of the HER2 protein. HER2 proteins are receptors on breast cells made by the HER2 gene. In about 25 percent of breast cancers, the HER2 gene makes too many copies of itself, and these extra genes ultimately make breast cells grow and divide in ways that are uncontrollable. HER2-positive breast cancers are more likely to spread and return than those that are HER2-negative.

• Oncotype DX score: The oncotype DX score helps doctors determine a woman’s risk of early-stage, estrogen-receptor positive breast cancer recurring and how likely she is to benefit from post-surgery chemotherapy. In addition, the score helps doctors figure out if a woman is at risk of ductal carcinoma in situ recurring and/or at risk for a new invasive cancer developing in the same breast. The score also helps doctors figure out if such women will benefit from radiation therapy or DCIS surgery.

Determining breast cancer stage is a complex process, but one that can help doctors develop the most effective course of treatment. More information is available at http://www.breastcancer.org.