Vemurafenib-related photosensitivity.

Increased photosensitivity is a common cutaneous adverse effect associated with the BRAF inhibitor vemurafenib. Clinically, it presents as an immediate sensation of heat and edematous erythema during sun exposure, as well as a sunburn reaction in terms of a late reaction. Phototesting has shown that the UVA range (320 nm to 400 nm), triggers both the immediate and the late reaction. In terms of pathogenesis, photochemical studies have suggested that exposure of vemurafenib to UVA radiation produces an UVA-absorbing photoproduct. In vitro studies on various cell models have also demonstrated that the phototoxic effects of vemurafenib are exclusively caused by UVA irradiation. This latter mechanism is probably responsible for the photosensitivity clinically observed in patients receiving vemurafenib. In addition, vemurafenib is able to inhibit ferrochelatase. The resulting increase in protoporphyrin IX has also been observed in some human studies involving the drug. However, it is yet unproven whether porphyrins actually contribute to the immediate skin reactions seen in individuals on vemurafenib, even though the clinical presentation is similar to that found in erythropoietic protoporphyria with a comparable pathomechanism. Other BRAF inhibitors, such as dabrafenib and encorafenib, are associated with significantly lower photosensitivity. It is essential that patients treated with vemurafenib are informed about immediate and delayed reactions potentially caused even by low doses of UVA. This includes counseling on photoprotective measures.