This page was reviewed under our medical and editorial policy by
Daniel Liu, MD, Plastic and Reconstructive Surgeon
This page was reviewed on September 20, 2022.
Tumors are often described by their size. The size of a breast tumor is an important factor in staging breast cancer. Doctors use a specific classification, known as the TNM (tumor, node, metastasis) system, to stage breast cancer. The T stands for tumor size, reported in millimeters or centimeters.
Breast cancer may be stage 0, 1, 2, 3 or 4, and the stage will depend on the size of the tumor, along with several other factors. Breast cancer staging also incorporates additional factors beyond the TNM staging system, such as hormone markers, because of the uniqueness of breast tissue. The doctor can explain why a cancer was given a particular stage.
Knowing the size of a tumor helps guide treatment. Different sized tumors may require different approaches. Additionally, knowing the initial size allows doctors to compare images taken after treatment to determine whether the tumor has shrunk or is responding to treatment.
A few studies have looked at typical tumor size upon diagnosis. In data from 819,647 patients diagnosed with breast cancer between 1990 and 2014, 93 percent of women had tumors under 50 mm in diameter, according to a study in Breast Cancer Research and and Treatment. In another study, in the American Journal of Roentgenology following 490 diagnosed breast cancer patients from 2016 to 2017, the average tumor size upon diagnosis of cancer was 1.4 cm for women who had annual mammograms and 1.8 cm for women who had exams only once every two years.
Tumor size is typically measured using millimeters or centimeters. For example, a tumor could be 2 centimeters or 20 millimeters. Common everyday foods may help with understanding measurements:
Tumor size is measured based on an imaging scan or surgical removal of the tumor. Tests such as mammograms or ultrasounds may be used to take images and measure the tumor, and often may be instrumental in first detecting the tumor. If the tumor is operable, meaning it may be safely removed during surgery, it will also be measured after removal. Tumors are measured at their widest point.
A tumor is given a TNM system number that corresponds to its size: T1 through T4. Some categories are broken down into more specific subtypes.
| Classification | Meaning |
|---|---|
| TX | The tumor size cannot be assessed. |
| T0 | There is no evidence of a primary tumor. |
| Tis |
Carcinoma in situ, non-invasive cancer confined within the ducts of the breast tissue that has not spread into the surrounding breast tissue.
Tis (DCIS) is ductal carcinoma in situ.
Tis (Paget) is Paget’s disease of the nipple that is not associated with tumor mass (invasive carcinoma or DCIS). |
| T1 | The tumor is 20 millimeters (2 centimeters) in diameter or less. T1mi tumors are less than 1 mm in diameter. T1a tumors are over 1 mm and no more than 5 mm in diameter. T1b tumors are over 5 mm and no more than 10 mm in diameter. T1c tumors are greater than 10 millimeters and no more than 20 millimeters. |
| T2 | The tumor is larger than 20 millimeters (2 centimeters) and no more than 50 millimeters (5 centimeters). |
| T3 | The tumor is bigger than 50 millimeters (5 centimeters). |
| T4 |
The tumor is any size and has grown into the skin or chest wall. T4d is inflammatory breast cancer. |