Breast Cancer Staging

As research gives us more information about breast cancer, the staging system is getting more complex and detailed – and more difficult for patients to understand.  A chart that lists the full breast cancer staging system is included in Understanding Your Pathology Report.  Stage and grade are different, but are sometimes confused by patients, and are major factors in determining treatment and prognosis. 

Stage is based on the size of the cancer, as well as whether it has spread beyond the breast to either the lymph nodes or distant sites in the body.  Breast cancer has two types of staging.  Clinical staging is based on tests done before surgery – the physical examination, mammograms, x-rays, CT scans and MRIs – that provide information on the size of the tumor and whether it may have spread.  Pathologic staging is based on the pathology of the surgical specimen – i.e., the pathologist's examination of the breast tissue and lymph nodes that are removed during surgery.

Although clinical staging is important in developing a treatment plan, your final pathologic staging defines your overall stage of cancer. Both clinical and pathologic staging are described using Roman numerals (I to IV). Stage I is the earliest stage of invasive breast cancer; Stage IV, the most advanced.

Doctors use the "TNM" system to describe overall tumor staging, which takes into account tumor size, lymph node involvement, and any evidence of metastatic disease.  In this system, the letters mean:

T refers to the primary tumor.  How large is it?  Where is it located?  Does it involve the overlying skin or underlying muscle?  Tumor size is rated from 0-4: T0 (no evidence of disease), Tis (includes in situ disease and Paget’s disease), T1 (describes the smallest invasive tumor, measuring up to 2cm), T3 (the largest invasive tumor, over 5cm), and T4 (describes whether the cancer involves the overlying skin or underlying muscle, as well as any inflammatory cancer).   

N refers to regional lymph node involvement.  For example, has the tumor spread to lymph nodes, how many, and which ones?  Lymph node involvement is classified as N0 (meaning no nodes are involved), N1 (1-3 nodes are involved), N2 (4-9 nodes are involved), and N3 (more than 10 lymph nodes involved).

M refers to distant metastasis.  Has the tumor spread to any other organs or parts of the body?  Metastasis is classified as MX (meaning that distant spread has not been evaluated), M0 (the cancer has not metastasized), and M1 (the cancer has metastasized to another part of the body).

Doctors assign a stage to the cancer by grouping the TNM information.  Each stage has one or more subgroups.  Additional information about these subgroups is available in Understanding Your Pathology Report.

Grade refers to the appearance and behavior of the cancer cells under the microscope.  Tumor grade is a way of describing the appearance and growth pattern of your tumor, and the extent to which the cancer cells differ from those of a normal cell.  Tumor grade helps predict how aggressive a cancer will be – that is, how likely it is to spread or to recur.  The more a cancer has lost its resemblance to normal cells, in appearance and behavior, the more rapidly it divides and, therefore, the more aggressive it is. Following a biopsy of your tumor, a pathologist examines it under the microscope and assigns it one of three grades.

Grade 1, or low-grade tumors, are those in which the cells look a little different from normal cells.  They grow in slow, well-organized patterns.  Relatively few are actively dividing.  Low grade tumors are also called "well differentiated."

Grade 2, or intermediate-grade/moderate-grade tumors, are those in which the cells look more abnormal, are less organized, and are growing and dividing at a more rapid rate.  They are also called "moderately differentiated."

Grade 3, or high-grade tumors, look very different from normal cells.  They grow in disorganized, irregular patterns, with many cells actively dividing and growing.  These tumors are also called "poorly differentiated" or "undifferentiated."

In general, low-grade tumors have a better prognosis, but because higher-grade tumors divide much more rapidly, they may respond better to chemotherapy and radiation.  These treatments usually work by killing cells that are actively dividing, which occurs more frequently in high grade tumors.

Next: Hormone Receptor Status.