Rare adverse events also have been reported in the literature, including vismodegib-induced pancreatitis in a 79-year-old patient treated for locally advanced, recurrent BCC that was cleared following cessation of therapy.26 Additionally, atypical fibroxanthoma was observed in an 83-year-old patient after 30 days of treatment with vismodegib for multiple BCCs.27 The development of other secondary malignancies, such as squamous cell carcinoma, melanoma, keratoacanthomas, and pilomatricomas, during or after the long-term use of vismodegib also have been described.28-35
Use of Vismodegib for Adnexal Skin Tumors
The role of the sonic Hh–PTCH pathway in the pathogenesis of adnexal tumors varies in the literature. Some studies propose the involvement of this pathway in the formation of adnexal tumors such as trichoblastoma, trichoepithelioma, and cylindroma, as in BCC. Various lines of evidence support this involvement. Firstly, in mice, the spontaneous generation of numerous BCCs, trichoblastomas, trichoepitheliomas, and cylindromas has been observed following constitutive activation of the sonic Hh–PTCH pathway.36 Secondly, in trichoepitheliomas, there have been positive results in molecular research into the tumor suppressor gene PTCH homologue 1, PTCH1, whose mutations cause constitutive activation of the sonic Hh–PTCH pathway.37 Thirdly, GLI138 and SOX939 transcription factors associated with the signaling pathway of sonic Hh–PTCH appear to have increased levels in adnexal carcinomas.19 Lepesant et al19 reported a notable clinical response to vismodegib in trichoblastic carcinoma. Baur et al40 reported successful treatment of multiple familial trichoepitheliomas with vismodegib. Nonetheless, more studies are required to assess the efficacy and reliability of vismodegib in the management of adnexal tumors.
Recommended Dose of Vismodegib Therapy
The vismodegib dosage that is approved by the FDA is 150 mg/d until disease progression or the development of intolerable side effects.4 Higher dosing regimens were evaluated with 270 mg/d and 540 mg/d. No added therapeutic benefit was noted with the increase in the dose, and no dose-limiting toxic effects were observed.41
Management of Vismodegib Side Effects
Managing patient expectations is a crucial step in improving dysgeusia. The experience of dysgeusia varies among patients; thus, patients should be instructed to adjust their diets according to their level of dysgeusia, which can be achieved by changing ingredients or dressings used with their diet. This step has been proven to be effective in overcoming vismodegib-related dysgeusia. Also, fluid taste distortion may lead to dehydration and an increase in creatine level. Thus, patients should be encouraged to monitor fluid intake. Moreover, a treatment hiatus of 2 to 8 months results in near-complete improvement of taste distortion.
For muscle spasms, quinine, treatment break for 1 month, gentle exercise of affected areas, or muscle relaxants such as baclofen and temazepam all are effective methods. For vismodegib-related alopecia, managing patient expectations is key; patients should be aware that hair may take 6 to 12 months or even longer to regrow. In addition, shaving less frequently helps improve alopecia.
For gastrointestinal disorders, loperamide with or without codeine phosphate is effective in resolving diarrhea, and metoclopramide is mostly adequate in treating nausea. Another adverse event is weight loss; weight loss of 5% or more of total body weight prompts dietetic referral. If weight loss persists, a treatment break might be needed to regain weight.
Overall, treatment breaks are sufficient to resolve adverse events caused by vismodegib and do not compromise efficacy of treatment. The duration of a treatment break should be considered before initiation. In one clinical trial, a longer treatment break was associated with fewer adverse effects without affecting the efficacy of treatment.42
Conclusion
Vismodegib provides an effective alternative to surgical intervention in the management of BCC. However, patients must be monitored vigilantly, as adverse events are common (>90%).