Merkel Cell Carcinoma Stages

After someone is diagnosed with Merkel cell cancer (MCC), 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 how much cancer is 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.

The earliest stage Merkel cell cancers are called stage 0 (or carcinoma in situ), and then range from stages I (1) through IV (4). As a rule, the lower the number, the less the cancer has spread. A higher number, like 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 most often used for Merkel cell 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): How large is the cancer? Has it grown into nearby structures or organs?
• The spread to nearby lymph nodes (N): Has the cancer spread to nearby lymph nodes ?
• The spread (metastasis) to distant sites (M): Has the cancer spread to distant lymph nodes or distant organs such as the lungs and skin?

The system described below is the most recent AJCC system as of January 2018.

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 get an overall stage. For more on this, see Cancer Staging.

The staging system in the table below uses the pathologic stage (also called the surgical stage). This is the staging system most often used for MCC. It's decided after testing the tissue taken out during an operation.

Sometimes, if surgery can't be done 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. The clinical stage will be used to help plan treatment. In some cases, though, the cancer has spread further than the clinical stage estimates, and may not predict the patient’s outlook as well as a pathologic stage. Clinical staging for MCC follows a separate staging system that's not covered in the table below. If your cancer has been clinically staged, ask your doctor for information about your specific stage.  

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*
0	Tis N0 M0	The cancer is only in the epidermis, the outermost skin layer (Tis). It has not spread to nearby lymph nodes (N0) or distant sites (M0). This stage is also known as carcinoma in situ (Tis).
I	T1 N0 M0	The cancer is no more than 2 centimeters (cm) across (about 4/5 inch). It has not spread to nearby lymph nodes (N0) or to distant sites (M0).
IIA	T2 or T3 N0 M0	The cancer is more than 2, but less than 5 cm (about 2 inches) across (T2) OR the tumor is more than 5 cm across (T3). It has not spread to nearby lymph nodes (N0) or to distant sites (M0).
IIB	T4 N0 M0	The cancer has grown into nearby tissues such as muscles, bones, or cartilage (T4). It has not spread to nearby lymph nodes (N0) or to distant sites (M0).
IIIA	T1, T2, T3, or T4 N1a(sn) or N1a M0	The cancer can be any size or may have grown into nearby tissues (T1, T2, T3, or T4) AND the cancer has spread to nearby lymph nodes, but this was found during a lymph node biopsy or surgery and was not seen on exams or imaging tests (N1a[sn] or N1a). It has not spread to distant sites (M0).
	OR
	T0 N1b M0	There's no sign of a primary cancer (T0) AND the cancer has spread to nearby lymph nodes, which was seen on exams or imaging tests and then confirmed by biopsy or surgery (N1b). It has not spread to distant sites (M0).
IIIB	T1, T2, T3, or T4 N1b, N2 or N3 M0	The cancer can be any size or may have grown into nearby tissues (T1, T2, T3, or T4) AND any of the following: It has spread to nearby lymph nodes, which was seen on exams or imaging tests and then confirmed by biopsy or surgery (N1b). It has spread toward a nearby lymph node area without reaching the lymph nodes (N2). This is called in transit metastasis. It has spread toward a nearby lymph node area (called in transit metastasis) and has reached the lymph nodes (N3). It has not spread to distant sites (M0).
IV	T0, T1, T2, T3 or T4 Any N M1	The cancer can be any size or may have grown into nearby tissues (T0, T1, T2, T3, or T4) AND might or might not have spread to nearby lymph nodes (Any N). It has spread to distant lymph nodes or organs, such as the lungs or skin (M1).

* The following categories are not listed on 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.