Hedgehog Pathway Inhibition for the Treatment of Basal Cell Carcinoma

Globally, basal cell carcinoma is the most commonly diagnosed cancer. While most cases are amenable to surgery, treatment options for advanced basal cell carcinoma, including locally advanced basal cell carcinoma and metastatic basal cell carcinoma, have proved more difficult. Recent advances regarding the role of hedgehog signaling in the pathogenesis of basal cell carcinoma and the identification of hedgehog pathway inhibitors have facilitated the development of treatment options with improved clinical outcomes. The hedgehog signaling pathway regulates development, cell proliferation, and tissue repair. The pathway is tightly regulated under normal physiological conditions. However, dysregulated hedgehog signaling in human cancers was first described in patients with basal cell carcinoma nevus syndrome and sporadic basal cell carcinoma, in which germline or somatic mutations in pathway components (e.g., smoothened [Smo] and patched-1) lead to constant activation. Subsequently, inhibitors blocking hedgehog signaling either at the level of Smo (i.e., vismodegib, sonidegib, patidegib, and itraconazole) or via an unknown mode of action (arsenic trioxide) were identified. The hedgehog inhibitor vismodegib is approved for the treatment of locally advanced basal cell carcinoma and metastatic basal cell carcinoma while sonidegib is approved for the treatment of locally advanced basal cell carcinoma in the USA and Europe; and for locally advanced basal cell carcinoma and metastatic basal cell carcinoma in Switzerland and Australia. The most common treatment-emergent adverse events associated with approved hedgehog inhibitors include muscle spasms, dysgeusia, and alopecia. This review addresses the challenges associated with appropriately diagnosing locally advanced basal cell carcinoma, provides an overview of hedgehog signaling in basal cell carcinoma, and discusses the pharmacology of hedgehog inhibitors and their efficacy, and adverse events associated with hedgehog inhibitor use, and their management.