Nonmelanoma skin cancer (NMSC) is the most common malignancy worldwide, and its incidence continues to increase. More than 5 million NMSCs are estimated to occur annually in the United States alone.1 There are more cases of basal cell carcinoma (BCC) than all other cancers combined, with squamous cell carcinoma (SCC) being the second most common cancer in the United States.1-3 The rising incidence of NMSCs highlights the importance of investigating additional treatment options with fewer side effects, better cosmetic outcomes, and better efficacy.1
Originally, treatment options for NMSCs largely relied on destructive and surgical methods. Basal cell carcinoma and SCC commonly are treated with cryosurgery; electrodesiccation and curettage; or more definitive surgical options, including excision and Mohs micrographic surgery (MMS). Over time, topical agents such as 5-fluorouracil, imiquimod, ingenol mebutate, and various forms of aminolevulinic acid (ALA) for photodynamic therapy (PDT) were included for superficial lesions as well as field treatment. The development of oral hedgehog (Hh) inhibitors, such as vismodegib, offered a promising alternative to patients with advanced disease. Each treatment has its own specific indications and side effects; thus, there is always room for novel therapeutic approaches. We review new and potential treatments from 2018 and beyond. Although only 5% of SCCs become locally advanced, recur, or metastasize, and 0.4% to 0.8% of BCCs progress to advanced disease, many of the newer studies target advanced NMSCs, given their life-threatening and debilitating nature.4,5 Similarly, the incidence of nevoid basal cell carcinoma (NBCC) syndrome is as low as 1 in 57,000 to 1 in 164,000 but continues to be studied because of its morbidity and the potential to contribute new treatment options for BCC in the general population.6
Topical Therapy
Sonidegib
Basal cell carcinoma proliferation is a result of an unregulated Hh pathway that is initiated when the Hh ligand binds to the patched 1 protein (PTCH1).7-11 Patched 1 protein normally inhibits the smoothened (SMO) transmembrane receptor protein, decreasing the signaling cascade. In BCCs, there is a loss of PTCH1 function, effectively increasing the Hh pathway activity. Sonidegib is an Hh inhibitor that in turn prevents inhibition of PTCH1 in an attempt to reregulate the pathway.7-11 Although sonidegib is known for its 2015 approval by the US Food and Drug Administration (FDA) as a systemic therapy for locally advanced BCCs,12 one study investigated a topical formulation on 8 patients with NBCC syndrome.13 Patients were treated twice daily with sonidegib cream 0.75% for 4 weeks in a double-blind, randomized, vehicle-controlled study. A total of 27 BCCs were randomized and treated with either vehicle or sonidegib. A biopsy was taken at the end of the study of 1 sonidegib-treated and 1 vehicle-treated BCC lesion per patient. Of the 13 sonidegib-treated BCC lesions, 3 (23.1%) showed complete response, 9 (69.2%) showed partial response, and 1 (7.7%) showed no response vs 13 of 14 (92.8%) lesions that did not respond to the vehicle. Patients tolerated the treatment well without skin irritation or signs of local or systemic side effects.13 Topical sonidegib should be further investigated as an adjunct or in different vehicles given the successful regression of BCCs and its minimal side-effect profile.
Systemic Therapy
Cemiplimab
Cemiplimab is a human monoclonal antibody against programmed death receptor 1 (PD-1) that was FDA approved in September 2018 for the treatment of metastatic cutaneous SCC.14 Programmed death receptor 1 is found on T lymphocytes, B lymphocytes, and macrophages, which normally assist in the immune response to tumor cells. However, programmed cell death ligand 1 (PD-L1) and programmed cell death ligand 2 (PD-L2) are found on tumor cells and bind to PD-1. Cemiplimab prevents PD-1 from binding to PD-L1 and PD-L2, allowing an appropriate immune response.14,15 A phase 1 clinical trial of cemiplimab showed a 50% (13/26) response rate.16 The phase 2 trial included patients with advanced SCC, but the primary analysis only considered patients with metastatic SCC. Phase 2 results showed a 47.5% (28/59) response rate. Patients received intravenous cemiplimab 3 mg/kg once every 2 weeks for up to 48 weeks in phase 1 and up to 96 weeks in phase 2. Both phases of the trial showed a response to treatment lasting longer than 6 months in more than 50% of patients. The most common adverse events were diarrhea, fatigue, nausea, constipation, and rash.16
Although immune-mediated adverse reactions are rare, they can occur given cemiplimab’s mechanism of action and may range from severe to fatal. Examples of immune-mediated adverse reactions that occurred during the study included pneumonitis, colitis, hepatitis, adrenal insufficiency, hypophysitis, hypothyroidism, hyperthyroidism, type 1 diabetes mellitus, nephritis with renal dysfunction, and immune-mediated dermatologic reactions.14 It is important to monitor for immune-mediated adverse reactions and address them immediately once detected.
Other PD-1 Inhibitors
Although PD-1 inhibitors have been studied in advanced SCCs, their clinical data are limited for BCCs.17 Prior to 2018, there was a small number of case reports of patients with BCC with partial to exceptional response to PD-1 inhibitors. Recently, 2 additional case reports were published with contrasting outcomes using 2 different PD-1 inhibitors. An elderly patient with metastatic non–small cell lung cancer was treated with nivolumab after failing chemotherapy. She subsequently developed a BCC on the nose that was resected but recurred 2 months later despite continuing nivolumab.17 Another case report detailed a patient with a history of BCC on the shoulder excised 5 years prior who presented with recurrence on the sternum and clavicle.18 One year later the patient was found to have BCC metastases to the lung. After progression of disease despite vismodegib and recurrence of BCC with taladegib, the patient was then placed on pembrolizumab. At 6 weeks and 12 months, computed tomography showed resolution of multiple lung lesions. Sixteen weeks after initiation of pembrolizumab treatment, spinal metastases were found, but the treatment was continued because of the improvement in the lung metastases.18
Taladegib
Taladegib is a SMO antagonist that has been through a phase 1 trial in patients with advanced cancer, including treatment-naive and previously treated BCCs.19 Eighty-four patients were treated to examine the safety profile and determine an appropriate phase 2 dose and administration schedule. The maximum tolerable dose was determined to be 400 mg because of dose-limiting toxicities. All clinical responses were in patients with BCCs (47/84 [55.9%] patients), with a response rate of 46.8%. Eleven of 16 (68.8%) Hh-treatment–naive patients and 11 of 31 (35.5%) patients previously treated with Hh responded to taladegib. Common adverse events were dysgeusia, fatigue, nausea, and muscle spasms.19 Although vismodegib is an FDA-approved SMO antagonist since 2012, treatment resistance and tolerability issues have been continuing concerns.20,21 Taladegib is a potential alternative that may be found to have improved pharmacodynamics and pharmacokinetics. Not only did in vitro studies show a preferable protein-binding profile with taladegib, but it also displayed dose proportionality, while vismodegib has been known to have nonlinear pharmacokinetics.19