Immunohistochemical markers of advanced basal cell carcinoma: CD56 is associated with a lack of response to vismodegib

Background: Vismodegib is an effective treatment for advanced basal cell carcinoma (BCC), but primary resistance to vismodegib remains to be elucidated. Alternative approaches are warranted to help selecting patients most likely to be responsive to treatment. The identification of immunohistochemical markers may support this perspective, as well as better understanding of resistance mechanisms. Objectives: To determine the level of expression of CD56, PDGF-R, CD117, MMP9, TIMP3, and CXCR4 in advanced BCC, and explore whether expression levels are associated with non-response to vismodegib. Materials and methods: A cross-sectional study was conducted. Immunohistochemical markers were selected based on their roles in tumour proliferation and/or migration in skin tumours. Tissue samples included pretreatment advanced BCC samples from patients treated with vismodegib, with an available response after six months of treatment. Regression optimised models were used to build hypotheses regarding a possible association between expression levels and non-response to vismodegib, which was then tested by logistic regression. Results: Twenty-three patients were included. The percentage of samples expressing markers ranged from 43.5% (CD117) to 91.3% (CXCR4). CD56 expression was significantly associated with an increased risk of non-response to vismodegib (OR = 5.5; CI 95%: 3.4-29.8; p = 0.0488); a similar association was suggested for CXCR4 (p = 0.066), but not identified for other markers. Conclusion: These results provide a better understanding of the expression of immunohistochemical markers in advanced BCC. Further detailed analysis of CD56 expression may provide insights into guiding further investigation of the correlation between this marker and non-response to vismodegib.