Skin Cancer: Merkel Cell Carcinoma

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Early Detection, Diagnosis, and Staging TOPICS

How are Merkel cell carcinomas staged?

The stage of a cancer is a description of how widespread it is. For Merkel cell carcinoma (MCC), this includes its size and location, whether it has grown into nearby tissues or bones, whether it has spread to the nearby lymph nodes or any other organs, and certain other factors.

The stage is based on the results of physical exams, any biopsies that have been done (including sentinel lymph node biopsy), and any imaging tests (CT, MRI, PET scan, etc.) that have been done. These tests are described in the section “How is Merkel cell carcinoma diagnosed?

The stage of the cancer is very important in planning treatment and estimating a person’s prognosis (outlook).

The American Joint Committee on Cancer (AJCC) TNM system

A staging system is a standard way to sum up how far a cancer has spread. Different staging systems have been used for MCC in the past, but the system now used most often is the American Joint Commission on Cancer (AJCC) TNM system.

Physical exams and other tests may be used to assign T, N, and M categories and a grouped stage. The TNM system for staging contains 3 key pieces of information:

  • T stands for the main (primary) tumor (its size and whether it has grown into nearby tissues such as muscles or bones).
  • N stands for spread to nearby lymph nodes (small bean-sized collections of immune system cells, to which cancers often spread first).
  • M is for metastasis (spread to distant organs). The most common sites of spread are the liver, lungs, bones, and brain.

T categories

The possible values for T are:

TX: The main (primary) tumor cannot be assessed.

T0: No evidence of primary tumor. (For example, the cancer was first found in the lymph nodes, but the main tumor itself can’t be found.)

Tis: Carcinoma in situ: the tumor is still confined to the epidermis, the outermost skin layer. (This is very rare for MCC.)

T1: The tumor is 2 centimeters (cm) across (about 4/5 inch) or smaller.

T2: The tumor is larger than 2 cm across, but it is less than 5 cm (about 2 inches) across.

T3: The tumor is larger than 5 cm across.

T4: The tumor has grown into nearby tissues such as muscles, bones, or cartilage.

N categories

It’s important to know whether the cancer has spread to nearby lymph nodes. Many times this can happen without the lymph nodes becoming enlarged (or otherwise abnormal), so a sentinel lymph node biopsy is an important part of staging for most patients. The possible values for N depend in part on whether or not a sentinel lymph node biopsy was done:

NX: Nearby lymph nodes cannot be assessed.

N0: No spread to nearby lymph nodes.

cN0: The nearby lymph nodes do not feel or look abnormal (including on imaging tests), but the nodes have not been biopsied to check for cancer cells.

pN0: The nearby lymph nodes have been biopsied and no cancer was found in them.

N1a: The cancer has spread to nearby lymph nodes, but this was found during a lymph node biopsy and was not noticed on exams or imaging tests.

N1b: The cancer has spread to nearby lymph nodes, which was noticed on exams or imaging tests (and then confirmed by biopsy).

N2: The cancer has spread toward a nearby lymph node area without reaching the lymph nodes. This is called in transit metastasis.

M categories

The M values are:

M0: No spread to distant organs.

M1a: The cancer has spread to other areas of skin, to tissues under the skin, or to distant lymph nodes.

M1b: The cancer has spread to the lungs.

M1c: The cancer has spread to any other organ(s).

Stage grouping

Once the T, N, and M groups have been determined, they are combined in a process called stage grouping to give an overall stage, using 0 and the Roman numerals I to IV (1 to 4). Some stages are divided further using capital letters. In general, patients with lower stage cancers tend to have a better outlook for a cure or long-term survival.

Stage 0

Tis, N0, M0: The MCC is in situ, meaning that it is only in the epidermis (Tis). It has not been found in nearby lymph nodes (N0) or in distant organs (M0).

Stage IA

T1, pN0, M0: The main tumor is no more than 2 cm across (T1). Cancer has not been found in nearby lymph nodes even after looking with a biopsy (pN0). It has not spread to distant organs (M0).

Stage IB

T1, cN0, M0: The main tumor is no more than 2 cm across (T1). The cancer does not seem to have spread to nearby lymph nodes, but a lymph node biopsy has not been done (cN0). It has not spread to distant organs (M0).

Stage IIA

T2 or T3, pN0, M0: The main tumor is larger than 2 cm across (T2 or T3). Cancer has not been found in nearby lymph nodes even after looking with a biopsy (pN0). It has not spread to distant organs (M0).

Stage IIB

T2 or T3, cN0, M0: The main tumor is larger than 2 cm across (T2 or T3). The cancer does not seem to have spread to nearby lymph nodes, but a lymph node biopsy has not been done (cN0). It has not spread to distant organs (M0).

Stage IIC

T4, N0, M0: The main tumor has grown into nearby tissues such as muscle, bone, or cartilage (T4). The cancer has not been found in nearby lymph nodes (N0) or distant organs (M0).

Stage IIIA

Any T, N1a, M0: The main tumor can be of any size and may or may not have grown into nearby tissues (any T). The cancer has spread to nearby lymph nodes, but this was found during a lymph node biopsy and was not noticed on exams or imaging tests (N1a). There is no distant spread (M0).

Stage IIIB

Any T, N1b or N2, M0: The main tumor can be of any size and may or may not have grown into nearby tissues (any T). The cancer has spread to nearby lymph nodes, which was noticed on exams or imaging tests and then confirmed by biopsy (N1b), OR the cancer has spread toward a nearby lymph node area without reaching the lymph nodes (N2). There is no distant spread (M0).

Stage IV

Any T, any N, M1(a, b, or c): The main tumor can be of any size and may or may not have grown into nearby tissues (any T). The cancer may or may not have spread to nearby lymph nodes (any N). The cancer has spread to other parts of the body, such as areas of skin, tissues under the skin, distant lymph nodes, or other organs in the body (M1).


Last Medical Review: 12/31/2013
Last Revised: 12/31/2013