Squamous cell carcinoma (SCC) is a cancer originating from squamous cells, flattened, scale-like cells found throughout the body. It is characterized by uncontrolled growth of these cells, forming abnormal tissue. SCC is a common form of skin cancer, but it can also develop in other areas where squamous cells are present.
The Normal Squamous Cell
Normal squamous cells are thin, flat, and resemble scales. They are part of the epidermis, the outermost layer of the skin, where they continuously shed as new cells form beneath them. These cells also line the surfaces of hollow organs and the respiratory and digestive tracts.
Their primary function is to provide a protective barrier. Squamous cells are found in numerous locations, including the outer layer of the skin, the lining of the mouth, throat, esophagus, and lungs. They are also present in the cervix, anus, and bladder.
How Squamous Cells Become Cancerous
Squamous cells transform into cancerous cells primarily due to DNA damage that leads to abnormal changes, or mutations, within their genetic code. This damage often results from prolonged exposure to ultraviolet (UV) radiation, whether from sunlight or tanning beds, which directly induces specific “UV signature” mutations in the DNA. These genetic alterations disrupt the normal cell renewal process, causing abnormal cells to accumulate and form cancerous lesions.
Human papillomavirus (HPV) infection is another significant risk factor, particularly for squamous cell carcinomas of the head and neck, as well as the anogenital region. Chronic inflammation, such as that associated with long-standing wounds, ulcers, or certain infections, can also contribute to cellular transformation by promoting uncontrolled cell growth. Additionally, a weakened immune system, certain chemical exposures like arsenic, and a history of severe sunburns can increase the likelihood of these mutations. Pre-cancerous changes, such as actinic keratoses, which are lesions of atypical epidermal keratinocyte dysplasia, can also progress to squamous cell carcinoma, with an estimated annual progression rate of 0% to 0.075% per lesion.
The Behavior of Cancerous Squamous Cells
Once squamous cells become cancerous, they exhibit uncontrolled proliferation, meaning they multiply excessively and without regulation. This rapid and abnormal cell division leads to the formation of tumors. These cancerous cells can invade surrounding healthy tissues, breaking through the normal tissue boundaries.
In more advanced stages, these cells can spread to distant parts of the body, a process called metastasis. This occurs when cancer cells break away from the primary tumor, travel through the bloodstream or lymphatic system, and form new tumors in other organs, such as the lymph nodes, lungs, or bones. Cellular features distinguishing cancerous squamous cells from normal ones include atypical morphology, where cells show variations in size and shape, and large, often vesicular, nuclei that are frequently enlarged and hyperchromatic. They also display increased mitotic activity, indicating frequent and often abnormal cell division. Abnormal keratinization, where cells produce keratin in a disorganized manner, and the presence of keratin pearls, which are concentric layers of keratin surrounded by abnormal squamous cells, are also characteristic features.
Detecting Squamous Cell Carcinoma Cells
Detecting squamous cell carcinoma involves a biopsy, where a tissue sample from a suspicious area is removed. This procedure can often be performed in an outpatient setting, and the tissue is then sent to a pathology laboratory for microscopic examination. Pathologists, medical professionals specializing in diagnosing diseases, examine these samples under a microscope.
Pathologists look for specific cellular features to confirm the presence of squamous cell carcinoma. Evidence of invasion into surrounding tissues, such as the dermis, is also a diagnostic indicator.