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, the stage is based on the cancer’s 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.
Basal cell skin cancer is almost always cured before it spreads to other organs, so it is seldom staged unless the cancer is very large. Squamous cell cancers have a greater (although still 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 “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 staging 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. The TNM system is based on 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 (bean-sized collections of immune system cells, to which cancers often spread first).
- M is for metastasis (spread to distant organs).
TX: The main (primary) tumor cannot be assessed.
T0: No evidence of primary tumor.
Tis: Carcinoma in situ (the 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: The tumor is larger than 2 cm across, or is any size with 2 or more high-risk features.
T3: The tumor has grown into facial bones, such as the jaw bones or bones around the eye.
T4: The 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.
- The tumor is thicker than 2 millimeters (mm).
- The tumor has invaded down into the lower dermis or subcutis (Clark level IV or V).
- The tumor has grown into tiny nerves in the skin (perineural invasion).
- The tumor started on an ear or on a part of the lip.
- The tumor cells look very abnormal (poorly differentiated or undifferentiated) under a microscope.
NX: Nearby lymph nodes cannot be assessed.
N0: The cancer has not spread to nearby lymph nodes.
N1: The cancer has 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: The cancer has 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: The cancer has 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: The cancer has 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: The cancer has spread to any nearby lymph node that is larger than 6 cm across.
M0: The cancer has not spread to distant organs.
M1: The cancer has spread to distant organs.
To assign an overall stage, the T, N, and M categories are 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 outlook 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: 04/02/2015
Last Revised: 02/01/2016