Unlike many types of cancers with a numerical staging system, squamous cell skin cancer (SCSC) more often follows a unique categorization based on the risk assessment of the primary tumor. This unique staging system puts most SCSCs into one of two groups: Low-Risk and High-Risk. Treatment options are then based on each category to prevent recurrence and spread beyond the initial tumor. Tumor location and size are the basis for this categorization.

Very rarely are SCSC tumors metastatic and have spread from the initial site. Some tumor cells may be detected in regional lymph nodes. Tumors that spread far beyond the primary site require more complicated treatment procedures. The highest risk factor you have present will be used to assign your cancer stage.

Local, Low-Risk Squamous Cell Skin Cancer

SCSCs that are categorized as low-risk are also called primary and are not recurrent tumors. They are more likely to develop on the trunk and extremities and are less than two centimeters (cm) in size and two millimeters (mm) in depth. These small tumors are unlikely to return or become metastatic. They have well-defined edges and are not invasive.

Local, High-Risk Squamous Cell Skin Cancer

The group of SCSCs categorized as high-risk have an elevated risk of local recurrence. They are more likely to metastasize than the low-risk group. These tumors are greater than two mm in size and are associated with a poorer disease-specific survival. High-risk SCSCs have poorly defined edges and grow rapidly.

High-risk SCSCs will often appear on the head and neck area, including the ears and lips. Besides the head and neck, SCSCs that develop on the hands and feet, or the pretibial (shin), and anogenital (anus and genital) areas are also at greater risk of local recurrence and nodal metastasis, independent of size. Any tumors that have returned are defined as high risk. Tumors that have invaded deeply into the skin dermis or subcutaneous fat at a depth of greater than two mm are also considered high risk.

High-risk categorization may also apply to people with immunosuppression from organ transplantation, HIV, lymphoma, or chronic lymphocytic leukemia (CLL). If the SCSC occurs on a site of chronic inflammation or prior radiation therapy, it is considered high-risk. Neurological symptoms could be apparent in people with high-risk SCSC.

Regional or Metastatic Squamous Cell Skin Cancer

In rare cases, the SCSC can develop beyond the local, primary site on the skin. It may have spread in the area (regional) to lymph nodes or distant sites (metastasis). Among SCSC tumors less than or equal to two millimeters (mm) in thickness, the rate of metastasis is usually 0%. For SCSC tumors greater than two mm and up to six mm in thickness, the rate of metastasis is about 4%, and for tumors thicker than six mm, the rate is about 16%. Clinical examination of biopsies and images inside the body will confirm the extent of disease spread.