Squamous Cell Carcinoma (SCC) is the second most common type of skin cancer, arising from the flat, scale-like cells in the outermost layer of the skin. Most SCC diagnoses have a favorable outcome because the cancer is typically slow-growing and responds well to early treatment. The risk of SCC progressing to an aggressive, fast-spreading form is low, especially when detected early. Understanding its typical growth rate and the factors that influence its progression helps contextualize the overall risk.
Understanding Typical Growth Speed
The local growth of a typical, low-risk Squamous Cell Carcinoma is generally a slow process unfolding over months or even years. This slow rate of proliferation allows many early-stage SCCs to be detected and treated before they develop concerning characteristics. The rate of increase in size for an average SCC lesion is estimated to be between 0.1 to 0.3 centimeters per month.
A tumor may take many months, sometimes up to two years, to reach a size of just one centimeter across. This gradual expansion allows a significant window for detection and intervention. The speed of growth is mostly localized, meaning the tumor grows outward and downward at the site of origin, not spreading to distant parts of the body during this early phase.
Key Factors Determining Aggressiveness
While most SCCs are slow-growing, certain high-risk features increase their potential for aggressive behavior and faster progression. These features are identified through clinical examination and by a pathologist analyzing the biopsy sample. Poorly differentiated tumors are considered more aggressive because their cells look very abnormal compared to healthy skin cells, indicating a higher rate of mutation and division.
The depth of invasion is a significant factor. Tumors growing deeper than six millimeters or extending beyond the subcutaneous fat layer carry a higher risk of systemic spread. Tumors larger than two centimeters in diameter are also categorized as higher-risk because their size increases the likelihood of having invaded deeper tissues.
Certain body locations are associated with a greater risk of aggressive behavior, including the lip, ear, hands, feet, and areas of the central face. Specific microscopic findings, such as perineural invasion (cancer cells tracking along a nerve), increase the risk of spread. Patient-specific health factors also play a role, as individuals who are immunosuppressed—such as organ transplant recipients—have a higher chance of developing aggressive SCCs that grow and spread more rapidly.
The Timeline of Metastasis
Metastasis, the spread of SCC to distant sites, is a rare event, affecting only about three to nine percent of cutaneous cases. When an aggressive SCC spreads, the initial route is usually through the lymphatic system to the nearest cluster of lymph nodes. The progression of the disease is generally divided into two phases: the slow, initial growth of the primary tumor, and the potentially faster rate of spread once the cancer gains access to the lymphatic or vascular systems.
For high-risk tumors left untreated, the time frame from initial diagnosis to potential spread to the regional lymph nodes is often cited as approximately 12 to 24 months. Once the cancer invades the lymph nodes, its speed of progression through the body can accelerate compared to its initial local growth phase. Distant metastasis, the spread to internal organs like the lungs or liver, is the most advanced and least common outcome.