How are basal and squamous cell skin cancers staged?
The stage of a cancer is a description of how widespread it is. For skin cancers this includes its size and location, whether it has grown into nearby tissues or bones, whether it has spread to the lymph nodes or any other organs, and certain other factors.
Because basal cell skin cancer is almost always cured before it spreads to other organs, it is seldom staged unless the cancer is very large. Squamous cell cancers have a greater (although still quite small) risk of spreading, so staging may sometimes be done, particularly in people who have a high risk of spread. This includes people with suppressed immune systems, such as those who have had organ transplants and people infected with HIV, the virus that causes AIDS.
The tests and exams described in the section called “How are basal and squamous cell skin cancers diagnosed?” are the main ones used to help determine the stage of the cancer. In rare cases, imaging tests such as x-rays, CT scans, or MRI scans may be used as well.
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. This helps members of the cancer care team determine a patient's prognosis (outlook) as well as the best treatment options.
The system most often used to stage basal and squamous cell skin cancers is the American Joint Commission on Cancer (AJCC) TNM system.
Merkel cell carcinoma has a separate AJCC staging system, which is not described here.
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 tumor (its size, location, and how far it has spread within the skin and to nearby tissues).
- N stands for spread to nearby lymph nodes (small bean-shaped collections of immune system cells, to which cancers often spread first).
- M is for metastasis (spread to distant organs).
The possible values for T are:
TX: The main (primary) tumor cannot be assessed.
T0: No evidence of primary tumor.
Tis: Carcinoma in situ (tumor is still confined to the epidermis, the outermost skin layer).
T1: The tumor is 2 centimeters (cm) across (about 4/5 inch) or smaller and has no or only 1 high-risk feature (see below).
T2: Tumor is larger than 2 cm across, or is any size with 2 or more high-risk features.
T3: Tumor has grown into facial bones, such as the jaw bones or bones around the eye.
T4: Tumor has grown into other bones in the body or into the base of the skull.
High-risk features: These features are used to distinguish between some T1 and T2 tumors.
- Tumor is thicker than 2 millimeters (mm).
- Tumor has invaded down into the lower dermis or subcutis (Clark level IV or V).
- Tumor has grown into tiny nerves in the skin (perineural invasion).
- Tumor started on an ear or on non-hair-bearing lip.
- Tumor cells look very abnormal (poorly differentiated or undifferentiated) when seen under a microscope.
The possible values for N are:
NX: Nearby lymph nodes cannot be assessed.
N0: No spread to nearby lymph nodes.
N1: Spread to 1 nearby lymph node which is on the same side of the body as the main tumor and is 3 centimeters (cm) or less across.
N2a: Spread to 1 nearby lymph node which is on the same side of the body as the main tumor and is larger than 3 cm but not larger than 6 cm across.
N2b: Spread to more than 1 nearby lymph node on the same side of the body as the main tumor, none of which are larger than 6 cm across.
N2c: Spread to nearby lymph node(s) on the other side of the body from the main tumor, none of which are larger than 6 cm across.
N3: Spread to any nearby lymph node that is larger than 6 cm across.
The M values are:
M0: No spread to distant organs.
M1: Spread to distant organs.
To assign a stage, information about the tumor and whether it has spread to lymph nodes and other organs in the body is combined in a process called stage grouping. The stages are described using the number 0 and Roman numerals from I to IV. In general, patients with lower stage cancers tend to have a better prognosis for a cure or long-term survival.
Tis, N0, M0
T1, N0, M0
T2, N0, M0
T3, N0, M0
T1 to T3, N1, M0
T1 to T3, N2, M0
Any T, N3, M0
T4, any N, M0
Any T, any N, M1
Last Medical Review: 09/20/2012
Last Revised: 01/17/2013