Staging is a process of finding out how widespread a cancer is. Because basal cell cancer so rarely spreads to other organs, it is seldom staged unless the cancer is very large. Squamous cell cancers have a somewhat 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, "How are basal and squamous cell skin cancers diagnosed?" are the ones used to help determine the stage of the cancer.

A staging system is a way to summarize how far a cancer has spread. This helps members of the cancer care team to plan appropriate treatment and determine a patient's prognosis (outlook).

The American Joint Committee on Cancer (AJCC) TNM System

The system most often used to stage keratinocyte cancers (especially squamous cell skin cancer) 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 tumor (its size 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 that help the body fight infections and cancers).
• M is for metastasis (spread to distant organs).

The possible values for T are:

TX: Primary tumor cannot be assessed
T0: No evidence of primary tumor
Tis: Carcinoma in situ (tumor is still confined to the epidermis)
T1: The tumor is 2 centimeters (cm) across (about 4/5 inch) or smaller
T2: Tumor is larger than 2 cm across but smaller than 5 cm (about 2 inches)
T3: Tumor is larger than 5 cm across
T4: Tumor of any size that invades deeply into muscle, cartilage, or bone

The possible values for N are:

NX: Nearby lymph nodes cannot be assessed
N0: No spread to nearby lymph nodes
N1: Spread to nearby lymph nodes

The M values are:

MX: Presence of distant metastasis cannot be assessed
M0: No distant metastasis
M1: Distant metastasis is present

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.

Stage 0

Tis, N0, M0: Squamous cell carcinoma in situ, also called Bowen disease, is the earliest stage of squamous cell skin carcinoma. The cancer involves only the epidermis and has not spread to the dermis. In contrast, higher stage cancers involve both the epidermis and dermis.

Stage I

T1, N0, M0: The cancer is no larger than 2 centimeters across (about 4/5 inch). It does not invade deeply into muscle, cartilage, or bone and has not spread to nearby lymph nodes or other organs.

Stage II

T2 or 3, N0, M0: The cancer is larger than 2 cm across. It does not invade deeply into muscle, cartilage, or bone and has not spread to nearby lymph nodes or other organs.

Stage III

T4, N0, M0 or Any T, N1, M0: The cancer has grown into tissues beneath the skin (such as muscle, bone, or cartilage) and/or it has spread to nearby lymph nodes. The cancer has not spread to other organs such as the lungs or brain.

Stage IV

Any T, Any N, M1: The cancer can be any size and may or may not have spread to local lymph nodes. It has spread to other organs such as the lungs or brain.