Squamous cell carcinoma (SCC) is a common form of skin cancer that originates from the flat, scale-like cells in the outer layer of the skin, known as the epidermis. The rate at which these tumors grow is highly variable and depends on a multitude of biological and environmental factors. A single, definitive answer regarding the speed of growth is impossible, but observed timelines provide a clearer picture of its progression.
Understanding Squamous Cell Carcinoma
SCC is the second most frequent type of skin cancer, following basal cell carcinoma (BCC). It arises from the keratinocyte cells of the epidermis, often in areas that have received cumulative exposure to ultraviolet (UV) radiation over time. SCC is generally considered faster-growing and has a greater potential for spreading to distant sites than BCC.
The tumor typically presents as a scaly red patch, a firm lump, or an open sore that does not heal. SCC is classified based on its depth of invasion. In situ SCC, sometimes called Bowen’s disease, remains confined to the topmost layer of the skin, the epidermis. When the cancerous cells breach the basement membrane and invade the deeper layer, the dermis, it is considered an invasive SCC, which significantly increases the risk of aggressive behavior and metastasis.
The Variable Timeline of SCC Growth
The timeline for SCC growth is measured in months rather than weeks, but the range of speeds is wide. A common growth rate observed in less aggressive cutaneous SCCs is approximately 1 to 2 millimeters (mm) per month. Some tumors can take a year to become noticeable, while others may double in size in just a few months.
The concept of “doubling time” (DT) is used to quantify the rate of exponential growth in tumors. A growth rate greater than 4 mm per month is often used by clinicians as a cutoff point to identify rapidly progressing, high-risk SCCs.
Tumors exhibiting a growth rate above this 4 mm per month threshold are considered fast-growing and are associated with a shorter time to lymph node metastasis. For these tumors, the median time until lymph node metastasis may be as short as five months, compared to 17 months for slower-growing tumors. This shows that a distinct subset is capable of highly accelerated growth.
Key Factors Accelerating or Slowing Growth
The speed at which an SCC develops is determined by several specific biological and host-related factors. A significant accelerator of SCC growth is immunosuppression, which occurs in individuals with compromised immune systems, such as organ transplant recipients or HIV patients. The body’s reduced ability to detect and eliminate abnormal cells allows tumors to proliferate more rapidly and aggressively, leading to a higher risk of recurrence and metastasis.
The cellular characteristics of the tumor itself also strongly influence its speed. SCCs are classified by their degree of differentiation, which describes how much the cancer cells resemble normal skin cells. “Poorly differentiated” SCCs look least like normal cells, indicating a higher rate of uncontrolled division and a faster growth rate. Poor differentiation is associated with worse outcomes, including increased risk of disease-specific death.
Anatomical location also plays a role in determining growth aggressiveness. While most SCCs occur on sun-exposed areas, those that develop on sites of chronic inflammation, such as old scars or ulcers, or on mucous membranes tend to grow faster. A history of previous SCCs increases the risk of developing new lesions, and these recurrent tumors can sometimes exhibit accelerated growth patterns.
Implications of Rapid Growth
A fast-growing SCC carries significant clinical implications because increased speed correlates directly with a higher risk of adverse outcomes. Rapid progression means the tumor has less time to be detected and can invade deeper tissue layers more quickly. This local invasion makes subsequent surgical removal more complex, potentially requiring more extensive procedures and leading to greater tissue destruction.
The most concerning implication of rapid growth is the heightened potential for metastasis, or the spread of cancer to distant parts of the body. A high growth rate is strongly associated with an increased risk of spreading to regional lymph nodes.
Tumors growing faster than the 4 mm per month benchmark have a significantly higher risk of nodal progression. Recognizing and monitoring for any sign of rapid change in a skin lesion is a major factor in improving the long-term prognosis.