EGFR expression is predictive of a poor prognosis in feline cutaneous squamous cell carcinoma

Treatment of feline cutaneous squamous cell carcinoma (FCSCC) is challenging due to its highly infiltrative and local destructive behavior. Dysregulations of epidermal growth factor receptor (EGFR) signaling have been found in many human cancers, including SCC. EGFR expression by neoplastic cells has been associated with a poor prognosis and makes SCC an attractive target for EGFR inhibitor therapy. The aim of this study was to characterize EGFR expression in FCSCC and assess its prognostic role. Nineteen formalin-fixed paraffin-embedded excisional biopsies of FCSCC were tested for EGFR expression using immunohistochemistry. A scoring system that took into consideration the staining intensity as well as the percentage of positive tumor cells was used. Relationships between EGFR expression and histopathological parameters (degree of differentiation, mitotic activity), disease free interval (DFI) and overall survival at 24 months were further investigated. Fourteen out of 19 tumors (74%) were positive for EGFR, with great variation in intensity and proportion of labeled cells. EGFR expression was not correlated with tumor differentiation or mitotic activity. Nine cats (47%) died of tumor-related causes (mean survival time, 9 months). EGFR score was higher in the cases with a negative outcome (6.22 vs 3.75, P=0.0352). Positivity for EGFR was significantly associated to decreased DFIs (P=0.0037) and survival times (P=0.0221). Our data suggest that activation of the EGFR pathway is possibly involved in the progression of FCSCC. Additionally, EGFR expression carries a negative prognostic significance in these tumors and may provide a rationale for using EGFR inhibitors in association with conventional treatments.