Increased phototoxic burn tolerance time and quality of life in patients with erythropoietic protoporphyria treated with afamelanotide - a three years observational study.

Background: Erythropoietic protoporphyria (EPP) is an ultra-rare genetic disorder (prevalence 1:150`000) characterized by instant painful phototoxic burn reactions in skin exposed to visible light. Afamelanotide is the first clinically tested therapy effectively increasing the time EPP patients can spend in direct sunlight without developing symptoms and reducing the number and severity of phototoxic reactions.

Objectives: We report our data on real-world effectiveness of afamelanotide treatment in EPP and its phototoxic burn protection factor (PBPF).

Methods: We analysed clinical data collected between 2016 and 2018 in the Swiss EPP cohort (n = 39) on maximum phototoxic burn tolerance time (PBTT), i.e., maximum time spent in sunlight without phototoxic reaction, severity of phototoxic reactions as assessed by an 11-point Likert-type visual analogue scale (VAS), with 0 being no pain and 10 being the worst possible pain, and Quality of Life (QoL), as assessed with an EPP-specific instrument.

Results: Before treatment, the PBTT was median 10 min (IQR 5-20). Under treatment, PBTT increased to median 180 min (IQR 120-240). Individual PBPF increased 1.8- to 180-fold (full range, median 15). The pain severity of the worst phototoxic reaction before treatment was median 10 and under treatment median 6 (IQR 3-7). QoL at the end of the observation period in 2018 (with all the assessed patients under treatment) was 81.4% (IQR 69.4-93.4, n = 34). A 97.4% treatment adherence rate was observed.

Conclusion: Treatment of EPP patients with afamelanotide is highly effective under real-world conditions. We suggest PBTT as a clinical meaningful endpoint in further clinical trials.