Basal and Squamous Cell Skin Cancer Stages and Risk Groups

The stage of a basal or squamous cell skin cancer is a way of describing how large the cancer is and how far it has spread. Knowing the stage is important to help determine your treatment options and to get an idea of how likely the cancer is to come back after treatment.

Staging basal and squamous cell skin cancers

Staging is the process of figuring out if the cancer has spread, and if so, how far. The stage of a cancer describes how much cancer is in the body.

The stage of a basal or squamous cell skin cancer is based on the results of the physical exam, the skin biopsy (and any other biopsies), and imaging tests if they are done.

For basal cell skin cancers (BCCs), staging is rarely needed, because these cancers are almost always cured before they spread to other parts of the body.

Squamous cell skin cancers (SCCs) are more likely to spread (although this risk is still small), so determining the stage can be more important, particularly in people who are at higher risk. This includes people with weakened immune systems, such as those who have had organ transplants and people infected with HIV, the virus that causes AIDS. Most SCCs occur in the head and neck region. They tend to have a higher risk of recurring (coming back) or spreading compared to SCCs in other locations.

How is the stage determined?

The system most often used to stage basal and squamous cell skin cancers is the American Joint Commission on Cancer (AJCC) TNM system. The most recent version, effective as of 2018, applies only to squamous and basal cell skin cancers of the head and neck area (lip, ear, face, scalp, and neck). The stage is based on 3 key pieces of information:

• The size of the tumor (T) and if it has grown deeper into nearby structures or tissues, such as a bone
• If the cancer has spread to nearby lymph nodes (N)
• If the cancer has spread (metastasized) to distant parts of the body (M)

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 assign an overall stage. The earliest stage of skin cancer is stage 0 (also called carcinoma in situ, or CIS). The other stages range from I (1) through IV (4). As a rule, the lower the number, the less the cancer has spread. A higher number, such as stage IV, means cancer has spread more.

Although the AJCC system is most common, other staging systems have also been developed. For example, the Brigham and Women’s Hospital (BWH) tumor classification system uses different risk factors to stage squamous cell skin cancers of the head and neck area.

If your skin cancer is in the head and neck area, talk to your doctor about your specific stage. Cancer staging can be complex, so ask your doctor to explain it to you in a way you understand.

To learn more about how cancers are staged, see Cancer Staging.

Other factors that can affect a person’s outlook and treatment options

The stage of a skin cancer can help give an idea of how serious the cancer is likely to be, but other factors can also be important. Some of these include:

• The location of the tumor
• How fast the tumor is growing
• How well-defined the borders of the tumor are
• If the tumor is new or has come back (recurred)
• If the tumor has been causing symptoms, such as pain or itching
• How the cancer cells look under a microscope
• If the cancer cells have invaded small nerves, blood vessels, or lymph vessels in and around the tumor
• If the cancer is in a place that was previously treated with radiation
• If the person has a weakened immune system

Doctors look at these factors to help determine how likely it is that a skin cancer will come back after treatment (or spread to other parts of the body, in the case of squamous cell skin cancer).

Risk groups for basal and squamous cell skin cancers

The National Comprehensive Cancer Network (NCCN) is an alliance of many of the nation’s leading cancer centers that develops treatment guidelines for cancer care. The NCCN uses many of the factors above to divide both basal and squamous cell cancers into risk groups, which can be used to determine the best treatment options.

Basal cell skin cancer risk groups

BCCs are divided into 2 risk groups: high and low risk, based on how likely they are to come back after treatment.

BCCs are at high risk of coming back after treatment if they have any of the following features:

• The tumor is on the trunk (chest or back), arm, or leg (other than the front of the lower leg), AND it’s at least 2 centimeters (cm) across.
• The tumor is on any other part of the body (head, neck, hands, feet, or genital area), regardless of size.
• The tumor doesn’t have well-defined borders.
• The tumor is a recurrence (as opposed to a new tumor).
• The tumor is in a place that was previously treated with radiation.
• The tumor has an aggressive growth pattern (when seen under a microscope).
• Cancer cells have invaded small nerves in or near the tumor (known as perineural invasion).
• The person with BCC has a weakened immune system.

BCCs that don’t have any of these features are in the low risk group.

To learn more about how these risk groups might affect your treatment options, see Treating Basal Cell Carcinoma.

Squamous cell skin cancer risk groups

SCCs are divided into 3 risk groups, based on how likely they are to spread or to come back after treatment. 

SCCs in the very high risk group have an increased risk of both coming back after treatment and of spreading to another part of the body. They have at least one of the following features:

• The tumor is at least 4 centimeters (cm) across.
• The cancer cells look poorly differentiated (very abnormal) under a microscope.
• The cancer is labeled as a desmoplastic SCC (based on how it looks under a microscope).
• The tumor is more than 6 millimeters (mm) deep, or it has grown beyond the fat layer below the skin (subcutaneous fat).
• Cancer cells have invaded a nerve deeper than the dermis layer of the skin.
• Cancer cells have invaded a blood vessel or lymph vessel in or near the tumor.

SCCs in the high risk group have an increased risk of coming back after treatment. These cancers don’t have any of the very high risk features above, but they have at least one of the following features:

• The tumor is on the trunk (chest or back), arm, or leg (other than the front of the lower leg), AND it’s more than 2 cm but no more than 4 cm across.
• The tumor is on any other part of the body (head, neck, hands, feet, front of the lower leg, or genital area), regardless of size.
• The extent of the tumor isn’t well defined.
• The tumor is a recurrence (as opposed to a new tumor).
• The tumor is in a place that was previously treated with radiation, or it’s in a place where there’s been chronic (long-term) inflammation.
• The tumor is growing quickly.
• The tumor is causing neurologic symptoms, such as pain or itching.
• The cancer is labeled as acantholytic, adenosquamous, or metaplastic SCC (based on how it looks under a microscope).
• The tumor is 2 to 6 millimeters (mm) deep.
• Cancer cells have invaded small nerves in or near the tumor (known as perineural invasion).
• The person with SCC has a weakened immune system.

SCCs that don’t have any of the features in either group above are in the low risk group.

To learn more about how these risk groups might affect your treatment options, see Treating Squamous Cell Carcinoma of the Skin.