A randomized, double-blind, placebo-controlled phase 3 skin cancer prevention study of DFMO in subjects with previous history of skin cancer

Preclinical studies have shown the inhibition of ornithine decarboxylase (ODC) by α-difluoromethylornithine (DFMO) and resultant decreases in tissue concentrations of polyamines (putrescine & spermidine) prevents neoplastic developments in many tissue types. Clinical studies of oral DFMO at 500 mg/m 2 /day revealed it to be safe and tolerable and resulted in significant inhibition of phorbol ester-induced skin ODC activity. Two hundred and ninety-one participants (mean 61 y.o., 60% male) with a history of prior non-melanoma skin cancer (mean 4.5 skin cancers) were randomized to oral DFMO (500 mg/m 2 /day) or placebo for 4–5 years. There was a trend toward a history of more prior skin cancers in subjects randomized to placebo, but all other characteristics including sunscreen and NSAID use were evenly distributed. Evaluation of 1200-person years of follow-up revealed a new non-melanoma skin cancer (NMSC) rate of 0.5 events/person/year. The primary endpoint, new NMSC’s, was not significantly different between subjects taking DFMO and placebo (260 vs. 363 cancers, p=0.069, two-sample t test). Evaluation of basal cell (BCC) and squamous cell (SCC) cancers separately revealed very little difference in SCC between treatment groups but a significant difference in new BCC (DFMO 163 cancers; Placebo 243 cancers; expressed as event rate 0.28 BCC/person/year vs. 0.40 BCC/person/year, p=0.03). Compliance with DFMO was >90% and it appeared to be well tolerated with evidence of mild ototoxicity as measured by serial audiometric examination when compared to placebo subjects. Analysis of normal skin biopsies revealed a significant (p