ON THIS PAGE: You will learn about how doctors describe a cancer’s growth or spread. This is called the stage. Classification is also important in describing these diseases. Use the menu to see other pages.
Staging is a way of describing where the cancer is located, if or where it has spread, and whether it is affecting other parts of the body. Doctors use diagnostic tests to find out the cancer's stage, so staging may not be complete until all the tests are finished. Knowing the stage helps the doctor recommend what kind of treatment is best and can help predict a person’s prognosis, which is the chance of recovery. There are different stage descriptions for different types of cancers.
TNM staging system
One tool that doctors use to describe the stage is the TNM system. Doctors use the results from diagnostic tests and scans to answer these questions:
Tumor (T): How large is the primary tumor? Where is it located?
Node (N): Has the tumor spread to the lymph nodes? If so, where and how many?
Metastasis (M): Has the cancer spread to other parts of the body? If so, where and how much?
The results are combined to determine the stage of cancer for each person.
There are 5 stages: stage 0 (zero) and stages I through IV (1 through 4). The stage provides a common way of describing the cancer, so doctors can work together to plan the best treatments.
Here are more details on each part of the TNM system for thymic tumors:
Using the TNM system, the "T" plus a letter or number (0 to 4) is used to describe the size and location of the tumor. Tumor size is measured in centimeters (cm). A centimeter is roughly equal to the width of a standard pen or pencil.
Stage may also be divided into smaller groups that help describe the tumor in even more detail. Specific tumor stage information is listed below.
TX: The primary tumor cannot be evaluated.
T0 (T plus zero): No evidence of a primary tumor.
T1: The tumor is located only in the thymus or has grown into the nearby fatty tissues.
T1a: The tumor has spread into fat surrounding the thymus or
T1b: The tumor has grown into the lining of the lung next to the tumor (called mediastinal pleura).
T2: The tumor has grown into the nearby fatty tissue and into the sac around the heart, called pericardium.
T3: The tumor has spread to nearby tissues or organs, including the lungs, the blood vessels carrying blood into or out of the lungs, or the phrenic nerve, which controls breathing.
T4: The tumor has spread to nearby tissues or organs, including the windpipe, esophagus, or the blood vessels pumping blood away from the heart.
The “N” in the TNM staging system stands for lymph nodes. These small, bean-shaped organs help fight infection. Lymph nodes near where the cancer started are called regional lymph nodes. Lymph nodes in other parts of the body are called distant lymph nodes.
NX: The regional lymph nodes cannot be evaluated.
N0: The tumor has not spread into lymph nodes
N1: The tumor may have spread to nearby lymph nodes.
N2: The tumor has spread to lymph nodes deep in the chest cavity or neck.
The “M” in the TNM system describes whether the cancer has spread to other parts of the body, called metastasis.
M0 (M plus zero): The disease has not metastasized.
M1: The tumor has spread to other organs near the thymus, such as the lung and blood vessels.
M1a: The tumor has spread to the lining of the lung, called the pleura, or lining of the heart, called the pericardium
M1b: The tumor may have spread to the lining of the lung or the heart.
In addition to stage, thymic tumors can be classified into different categories developed by the World Health Organization (WHO). These categories are based on what the tumor cells look like under a microscope:
Thymoma. There are several classifications to describe thymomas:
Type A thymoma. This is also called spindle cell thymoma or medullary thymoma. The chance of recovery for people with type A thymoma is good. Nearly 100% of people with this type live at least 15 years after diagnosis.
Type AB thymoma. Also called mixed thymoma, type AB thymoma is similar to type A thymoma. However, type AB thymoma has lymphocytes in the tumor. The chance of recovery for people with type AB thymoma is also good. About 90% of people with this type live at least 15 years after diagnosis.
Type B1 thymoma. This is also known as lymphocyte-rich thymoma, lymphocytic thymoma, predominantly cortical thymoma, and organoid thymoma. This type of thymoma has many lymphocytes in the tumor, but the cells of the thymus appear healthy. The chance of recovery for people with type B1 thymoma is also good. About 90% of people with this type live at least 20 years after diagnosis.
Type B2 thymoma. Type B2 thymoma is also known as cortical thymoma and polygonal cell thymoma. This type of thymoma also has many lymphocytes, like type B1 thymoma. However, the thymus cells do not appear healthy. About 60% of people with this type live at least 20 years after diagnosis.
Type B3 thymoma. Type B3 thymoma is also known as epithelial thymoma, atypical thymoma, squamoid thymoma, and well-differentiated thymic carcinoma. This type of thymoma has few lymphocytes, and the thymus cells look abnormal. Approximately 40% of people with this type live at least 20 years after diagnosis.
Thymic carcinoma. Thymic carcinoma is more aggressive. Thymic carcinoma cells do not look like healthy thymus cells. Instead, the cells look like cancers that start in other parts of the body. This type of tumor is often advanced when diagnosed. About 35% of people with thymic carcinoma live at least 5 years after diagnosis. Around 28% of people with thymic carcinoma live at least 10 years.
Thymic neuroendocrine tumors (TNETs). This is a rare, aggressive type of cancer found in the thymus (see Introduction). You can learn more about neuroendocrine tumors in another section of this website. TNETs may be associated with other conditions that affect the endocrine system, like Cushing's syndrome and MEN1 syndrome. Because these types of tumors are rare, there is not enough data to estimate survival rates. However, current research indicates that these tumors can be treated like similar NETs in other parts of the body. There are several types of thymic neuroendocrine tumors:
Typical carcinoid tumors (TC). These are considered low-grade and about 20% of all TNETs are considered typical.
Atypical carcinoid tumors (AC). These are considered intermediate-grade. About 40 to 50% of all TNETs are considered atypical. The difference between TC and AC is the presence of dead cells in the tumor, which is called necrosis.
Large cell neuroendocrine tumors (LCNEC). These are considered high-grade and 15 to 25% of all TNETs are LCNEC tumors. These tumor cells grow quickly and about 75% of the tumors spread to other parts of the body.
Small cell carcinoma tumors (SCC). These are considered high-grade and the cells in SCC tumors look like small cell tumors in other parts of the body. About 10% of TNETs are SCC tumors and most are diagnosed after the tumor has already spread to other parts of the body.
It is important to remember that statistics on how many people are diagnosed with thymoma and thymic carcinoma are an estimate. The estimate comes from data based on people with this cancer in the United States each year. So, your own risk may be different. Doctors cannot say for sure how long anyone will live with thymoma or thymic carcinoma. Learn more about understanding statistics.
Sources: TNM system information used with permission of the American College of Surgeons, Chicago, Illinois. The original and primary source for this information is the AJCC Cancer Staging Manual, Eighth Edition (2017), published by Springer International Publishing. WHO classification information source is the National Cancer Institute.
Information about the cancer’s stage and classification will help the doctor recommend a specific treatment plan. The next section in this guide is Types of Treatment. Use the menu to choose a different section to read in this guide.