Cancer staging is a way of describing how extensive a cancer is. The stage is related to tumor size. It also relates to whether the cancer has spread from the original tumor to other parts of the body. The cancer stage helps you and your doctor to develop a treatment plan. It also provides information about survival. Squamous cell carcinoma (SCC) stages use a system called TNM.1,2 This cancer staging system is used by most hospitals and medical systems.3 Once your doctor has categorized the T, N, and M, these values are combined to assign a cancer stage.2
Stages of squamous cell carcinoma: TNM System
T - Primary Tumor: Size of the tumor, presence of high-risk features, invasion of facial or skeletal structures
N - Regional Lymph Nodes: Presence, location, and number of lymph nodes with cancer cells and the size of the metastatic tumor
M - Metastasis: Spread of cancer to other parts of the body
Features of T categories
The T categories describe the main tumor based on its thickness, the presence of high-risk features, and invasion.2 Your doctor begins to gather this information by doing a skin biopsy. If the tumor is invasive, you will need imaging tests.
- Size. The longest dimension of the tumor is measured in centimeters.
- Invasion. The tumor is categorized by how far it has invaded the body. Invasion of the facial bones is categorized as T3. Invasion of bones in the rest of the body or the base of the skull is T4. Your doctor determines this using magnetic resonance imaging (MRI) or computed tomography (CT) scan.
- High-risk features. High-risk features refer to the risk that the cancer returns (recurs) or spreads (metastasizes). High-risk features of SCC are:2
- > 2 mm thick or Clark level ≥ IV
- Growing around a nerve
- Located on the ear or lip
- Poorly differentiated or undifferentiated cells. Differentiation means how much the cancer cells look like the normal tissue that it came from. Poorly differentiated cells grow and spread more quickly.
T categories
- TX - Primary tumor cannot be assessed
- T0 - No evidence of a primary tumor
- Tis - Carcinoma in situ (the tumor is only in the epidermis)
- T1 - Longest dimension is ≤ 2 cm and tumor has <2 high-risk features
- T2 - Longest dimension is >2 cm or Tumor of any size with ≥2 high-risk features
- T3 - Tumor has invaded the jawbone, eye socket, or the skull around the ears and temple
- T4 - Tumor has invaded the skeleton or base of the skull
N categories
The N categories indicate whether cancer cells have spread to nearby lymph nodes.2 One sign of cancer spread is enlarged or swollen lymph nodes. Another sign is that the lymph nodes may appear abnormal on imaging tests.2 If your doctor suspects that cancer has spread to the lymph nodes, you will need a lymph node biopsy. The biopsy is done with fine needle aspiration or a core needle biopsy.
N Categories
M Categories
The M categories indicate whether the cancer has spread (metastasized) to distant parts of the body.2 Simply, 0 means no metastasis and 1 means metastasis.
M Categories
- M0 - No distant metastasis
- M1 - Distant metastasis
Assigning an overall stage
Once the cancer is characterized, the categories are combined to assign a stage.2 Generally speaking, the lower the stage, the better the chance for long-term cure and survival.
Anatomic Stage
What are Clark Levels?
The Clark Level is based on which layer of skin the tumor has invaded.4,5
Clark Level
- Level I - All tumor cells are confined to the epidermis (top layer of skin), above the basement membrane.
- Level II - Tumor passes through basement membrane and invades the top layer of the dermis (papillary dermis).
- Level III - Tumor fills the papillary dermis and has reached the border (interface) between the top (papillar) and bottom (reticular) layers of dermis.
- Level IV - Tumor invades the bottom layer (reticular) of the dermis.
- Level V - Tumor invaded the tissue under the skin (subcutaneous tissue)2