Thymus Cancer Stages

After someone is diagnosed with thymus cancer, doctors will try to figure out if it has spread, and if so, how far. This process is called staging. The stage of a cancer describes the extent of the cancer in the body. It helps determine how serious the cancer is and how best to treat it. Doctors also use a cancer's stage when talking about survival statistics.

Thymus cancer ranges from stages I (1) through IV (4). As a rule, the lower the number, the less the cancer has spread. A higher number, such as stage IV, means cancer has spread more. And within a stage, an earlier letter means a lower stage. Although each person’s cancer experience is unique, cancers with similar stages tend to have a similar outlook and are often treated in much the same way.

How is the stage determined?

The staging system used for thymus cancer is the American Joint Committee on Cancer (AJCC) TNM system, which is based on 3 key pieces of information:

• The extent (size) of the tumor (T): Has the cancer grown into nearby structures and if so, how far as it grown?
• The spread to nearby lymph nodes (N): Has the cancer spread to nearby superficial or deep lymph nodes?
• The spread (metastasis) to distant sites (M): Has the cancer spread to the outer linings of the lungs or heart or to distant organs?

The system described below is the most recent AJCC system effective January 2018.  This staging system is used to stage thymomas, thymic carcinomas and neuroendocrine tumors of the thymus.

Numbers or letters after T, N, and M provide more details about each of these factors. Higher numbers mean the cancer is more advanced. Once a person’s T, N, and M categories have been determined, this information is combined in a process called stage grouping to assign an overall stage. For more information see Cancer Staging.

The staging system in the table below uses the pathologic stage (also called the surgical stage). It is determined by examining tissue removed during an operation. Sometimes, if surgery is not possible right away or at all, the cancer will be given a clinical stage instead. This is based on the results of a physical exam, biopsy, and imaging tests (CT or MRI scan, x-rays, PET scan, etc) done before surgery.

Cancer staging can be complex, so ask your doctor to explain it to you in a way you understand.

AJCC Stage	Stage grouping	Stage description*
I	T1a N0 M0	The cancer has not spread into the outer layer of the thymus OR it has grown into the nearby fatty tissues but not into the mediastinal pleura (the thin layer covering the space between the 2 lungs) (T1a). It has not spread to nearby lymph nodes (N0) or to distant sites (M0).
	OR
	T1b N0 M0	The cancer has grown into the nearby fatty tissue and the mediastinal pleura (the thin layer covering the space between the 2 lungs) (T1b). It has not spread to nearby lymph nodes (N0) or distant sites (M0).
II	T2 N0 M0	The cancer has grown into the nearby fatty tissue and into the pericardium (the tissue sac containing the heart) (T2). It has not spread to nearby lymph nodes (N0) or distant sites (M0).
IIIA	T3 N0 M0	The cancer is growing into nearby tissues or organs, including the lungs, the vessels carrying blood into or out of the lungs, the main blood vessels taking blood away from the heart (the superior vena cava), or the phrenic nerve (the nerve that controls the diaphragm and breathing) (T3). It has not spread to nearby lymph nodes (N0) or to distant sites (M0).
IIIB	T4 N0 M0	The cancer is growing into nearby tissues or organs, including the trachea (windpipe), esophagus (feeding tube), or the main blood vessels pumping blood away from the heart (T4). It has not spread to nearby lymph nodes (N0) or distant sites (M0).
IVA	Any T N1 M0	The cancer might or might not have grown into nearby tissues or organs (Any T) AND has spread to nearby lymph nodes in the front chest cavity (N1). It has not spread to distant sites (M0).
	OR
	Any T N0 or N1 M1a	The cancer might or might not have grown into nearby tissues or organs (Any T) and might or might not have spread to nearby lymph nodes (N0 or N1). The cancer has spread to the pleura (lining of the lung) or the pericardium (lining of the heart) (M1a).
IVB	Any T N2 M0 or M1a	The cancer might or might not have grown into nearby tissues or organs (Any T) AND has spread to the lymph nodes deep in the chest cavity or the neck (N2) and might or might not have spread to the pleura (lining of the lung) or the pericardium (lining of the heart) (M0 or M1b).
	OR
	Any T Any N M1b	The cancer might or might not have grown into nearby tissues or organs (Any T), might or might not have spread to nearby lymph nodes in the chest cavity or neck (Any N), but has spread to the inside of the lungs or other distant organs (M1b).

* The following additional categories are not listed in the table above:

• TX: Main tumor cannot be assessed due to lack of information.
• T0: No evidence of a primary tumor.
• NX: Regional lymph nodes cannot be assessed due to lack of information. 

Other prognostic factors

The prognosis (the outlook for chances of survival) after treatment of a thymus cancer depends to a large extent on its stage. But other features are also important such as the type of thymus cancer (as described in What Is Thymus Cancer?) and whether the surgeon is able to remove the entire tumor.