Psoriasis is not a form of skin cancer. It is an immune-mediated chronic disease resulting from an overactive immune system mistakenly attacking healthy skin cells, which causes inflammation and rapid cell turnover. This article clarifies the fundamental differences between psoriasis and cancer and addresses potential cancer risks associated with the disease and its treatments.
Understanding Psoriasis
Psoriasis is characterized by the accelerated life cycle of skin cells, specifically keratinocytes, leading to a rapid buildup on the skin’s surface. Normally, skin cells mature and shed over 28 to 30 days, but in psoriasis, this process speeds up to just three to four days. This hyperproliferation causes the formation of thick, raised patches known as plaques, which are often red and covered with silvery-white scales.
The most common form is plaque psoriasis, typically appearing on the elbows, knees, scalp, and lower back. Psoriasis is a non-contagious, chronic condition that cannot be cured, but it can be managed effectively with various therapies. The abnormal cell growth remains localized and is considered benign.
Key Differences Between Psoriasis and Cancer
The fundamental difference between psoriasis and cancer lies in the nature of cellular growth. In psoriasis, the rapid cell division is a form of hyperplasia, an orderly, regulated increase in the number of normal cells. Although fast, these cells mature and behave predictably within the tissue boundaries of the skin.
Cancer, conversely, is defined by malignancy and neoplasia, the uncontrolled proliferation of abnormal cells that ignore normal growth limits. Cancerous cells do not mature and possess the ability to invade surrounding tissues and spread to distant organs, a process called metastasis. Psoriatic plaques do not invade underlying tissues or metastasize.
Factors That Increase Cancer Risk in Psoriasis Patients
While psoriasis itself is not cancerous, patients have a slightly increased risk for developing certain types of cancer, particularly non-melanoma skin cancer and lymphoma. This elevated risk is believed to be a combination of three factors: chronic inflammation, shared lifestyle risk factors, and specific treatments. Psoriasis is characterized by long-term, systemic inflammation, which can contribute to the development of malignancy over many years.
Chronic inflammation creates a microenvironment that can promote DNA damage and cell instability, linking the severity of the inflammatory disease to cancer risk. Furthermore, lifestyle factors common in people with psoriasis, such as smoking, alcohol consumption, and obesity, are independently linked to an increased risk of lung, liver, and other cancers.
Certain systemic treatments used for severe psoriasis also carry risks. Psoralen plus Ultraviolet A (PUVA) phototherapy is associated with a significantly increased risk of squamous cell carcinoma, even years after treatment has stopped. The immunosuppressant drug cyclosporine increases the risk of non-melanoma skin cancer, particularly for patients treated for more than two years. Monitoring the long-term safety profiles of newer treatments, such as biologics and small-molecule therapies, remains an ongoing area of research to minimize cancer risk.
Monitoring Skin Changes and Warning Signs
Since psoriasis patients already have chronic skin lesions, distinguishing a typical plaque from a potentially malignant lesion is an important aspect of care. Psoriatic plaques are usually symmetrical, slow-growing, and consistent in appearance, often appearing on elbows, knees, and the scalp. In contrast, skin cancer lesions often develop in sun-exposed areas and may present as a sore that does not heal.
Melanoma, the most dangerous form of skin cancer, often follows the “ABCDE” warning signs: Asymmetry, irregular Border, varied Color, a Diameter larger than six millimeters, and Evolving or changing over time. Basal cell carcinoma and squamous cell carcinoma can sometimes resemble a persistent, scaly, reddish patch. Regular, full-body skin examinations by a dermatologist are essential for early detection. Any new lesion that bleeds easily, changes rapidly, or looks significantly different from typical psoriatic plaques should be evaluated immediately.