P-363 Skin rash as a predictor of tumor response to EGFR inhibitors in advanced colorectal cancer

The epidermal growth factor receptor (EGFR) is overexpressed in 70-80% of patients with advanced colorectal cancer. The development of antibodies that target this receptor, cetuximab and panitumumab, lead to an increase in overall survival in this setting. During therapy with EGFR inhibitors, the most common toxicity is acneiform rash, and may represent an early biomarker of tumor shrinkage that might predict the effectiveness of EGFR inhibitors. The aim of this study is to assess the predictive value of skin rash in terms of response and overall survival (OS) in patients with advanced colorectal cancer treated with cetuximab and panitumumab. We conducted a retrospective study of patients with advanced colorectal cancer receiving EGRF inhibitors with cetuximab or panitumumab from January 2013 to January 2023. Using Cox regression, the predictive role of skin rash on OS, progression and response rate were obtained. A total of 101 patients were analyzed: median age was 65 years, 59% were male, 91% received cetuximab and 71% of the patients developed an acneiform rash. Median OS was 31.1 months. The occurrence of skin rash in patients treated with cetuximab or panitumumab was associated with reduced risk of death (HR 0.25, 95% CI 0.15-0.43, P < 0.00001) and increased chance of response (70% vs 15%, p=0.24). All the 6 patients who had a complete tumor response had skin toxicity. Skin rash is also a predictive factor for progression (HR 0.27, 95% CI 0.15-0-48, P < 0.00001). The introduction of EGFR inhibitors in the setting of advanced colorectal cancer provided an increase in OS. Skin toxicities are the most common adverse events with EGFR inhibitors. The acneiform rash is a good predictor of tumor response in EGFR inhibitors therapy. Though rarely life-threatening, these events impact quality of life, increase patient risk for infections, and may lead to inconsistent EGFRI administration, all of which may affect clinical outcomes. A promptly treatment is essential to avoid delays or interruption of therapy.