Staging is the process of finding out how far a cancer has spread. Your treatment and prognosis (the outlook for chances of survival) depend, to a large extent, on the cancer's stage.

Masaoka staging system

There is no single staging system for thymomas that all doctors agree on, perhaps because these tumors are so uncommon. The system most often used to stage thymomas is called the Masaoka system, although other systems exist. Staging in the Masaoka system is based on:

• the extent of disease as seen on imaging tests such as CT or MRI scans

• whether the surgeon finds the tumor hard to separate from nearby tissues (indicating the tumor is invasive)

• whether the doctor sees tumor cells beyond the thymus when looking at the tumor sample under the microscope

The Masaoka system separates thymomas into 4 stages.

Stage I: The thymoma is non-invasive. That is, it has not spread into the capsule (outer layer) of the thymus.

Stage II: The thymoma invades the capsule and/or beyond the capsule into the nearby fatty tissue or the mediastinal pleura (the thin layer covering the space between the two lungs).

Stage III: The thymoma extends into nearby tissues or organs of the lower neck or upper chest area, including the pericardium (covering around the heart), the lungs, or the main blood vessels going into or exiting from the heart.

Stage IVA: The thymoma has spread widely throughout the pleura (lining of the lungs and chest wall) and/or pericardium.

Stage IVB: The thymoma has spread to distant organs such as the liver or kidneys.

Resectable versus unresectable cancer

The Masaoka staging system divides thymomas into several groups that help give doctors an idea about a person's prognosis (outlook). But for treatment purposes, doctors often use a simpler system based on whether these cancers are likely to be resectable (where all visible tumor can be removed by surgery) or unresectable.

In general terms, almost all stage I and II thymomas, most stage III thymomas, and even some stage IV thymomas are potentially resectable, but there are exceptions. Resectability is based on whether the tumor appears to have grown into nearby tissues or spread to distant sites, as well as on whether or not a person is healthy enough to have surgery.

Surgery is typically part of the treatment plan whenever possible. In some cases, other forms of treatment such as radiation therapy or chemotherapy may be recommended as well.

Other prognostic factors

The prognosis (the outlook for chances of survival) after treatment of a thymoma depends to a large extent on its stage. But other features are important as well, such as its cellular classification (described in the section "What is thymus cancer?") and whether the surgeon is able to remove the entire tumor.

Survival rates for thymoma

Survival rates are a way for doctors to discuss and compare the prognosis (outlook) for patients, usually based on the stage of the cancer or other traits. For example, the 5-year survival rate refers to the percentage of patients who live at least 5 years after being diagnosed. Although many patients live much longer than this, it isn't always an indication that the cancer has been cured, as some thymus tumors are very slow growing, and others may return in some people several years after treatment.

Because these cancers are not common, it is hard to find accurate survival rates based on the stage of the cancer. The statistics below are derived from several different studies of these tumors. There are some important points to keep in mind when looking at survival rates such as these.

These numbers are derived from patients treated at least several years ago. Improvements in treatment since then mean that the survival rates for people now being diagnosed with these cancers may be higher.

Survival statistics can sometimes be useful as a general guide, but they may not accurately represent any one person's prognosis. A number of factors other than the stage of the cancer may also affect outlook, including the WHO classification of the tumor (see "What is thymus cancer?") and whether or not the tumor is completely resected. For example, the survival rates for thymic carcinoma tend to be lower than the numbers below.

Your doctor is likely to be a good source as to whether the numbers below may apply to you, as he or she is familiar with the aspects of your particular situation.

Stage	Five-year survival rate
I	90% to 100%
II	85% to 95%
III	70% to 80%
IV	40% to 60%

Last Medical Review: 05/18/2009
Last Revised: 05/18/2009