The incidence of cutaneous squamous cell carcinoma is on the rise worldwide, a trend largely attributed to aging populations and cumulative exposure to solar ultraviolet (UV) radiation, which remains the primary environmental risk factor for the disease. While the vast majority of cSCC cases are successfully managed through the surgical excision of the primary tumor, the disease carries a hidden danger. Approximately 3% to 5% of these primary tumors will eventually metastasize, spreading to lymph nodes or distant organs. Once the cancer reaches this stage, the prognosis for the patient drops significantly, and the available treatment options become increasingly limited and less effective. Despite its reputation as a generally curable condition, cSCC is estimated to account for nearly 25% of all annual deaths related to skin cancer, highlighting a critical gap in early detection and specialized care for high-risk patients.
The search for reliable molecular markers has become a priority for oncologists specializing in dermatology. Lead investigator Veli-Matti Kähäri, MD, PhD, who works within the Department of Dermatology and the FICAN West Cancer Research Laboratory at the University of Turku, noted the current limitations in the field. He explained that there are presently no established molecular markers used in routine clinical practice that can accurately predict which primary cSCC tumors are likely to metastasize. This leaves doctors relying on tumor size, depth, and location to guess at the risk, which is often insufficient for catching the most aggressive cases before they spread. Dr. Kähäri emphasized that there is an urgent and ongoing need for predictive biomarkers that can clarify a patient’s prognosis and serve as targets for the development of new, more effective therapies for metastatic disease.
To address this need, the research team turned their attention to the complement system, an ancient and essential component of the human innate immune system. Traditionally, the complement system is understood as a defense mechanism—a series of proteins that work together to identify and destroy invading pathogens or clear out damaged cells. It is often described as a tumor-suppressing cytolytic mechanism. However, recent scientific inquiries across various types of cancer have begun to reveal a darker side to this immune response. In certain contexts, the complement system can be "hijacked" by a tumor, contributing to cancer progression and metastasis by fostering chronic inflammation or inducing a state of immunosuppression that allows the tumor to hide from the body’s natural defenses.
The Finnish researchers specifically focused on the interaction between a signaling molecule called C5a and its corresponding protein receptor, C5aR1. C5a is a potent inflammatory mediator, and its receptor, C5aR1, is typically found on the surface of various immune cells. In the context of the current study, the investigators sought to understand how this relationship functioned within the specific environment of cutaneous squamous cell carcinoma. They hypothesized that the activation of C5aR1 might be a key driver in the transition of a localized skin tumor into an invasive, life-threatening malignancy.
