A total of 334 subjects were enrolled over two years into the placebo run-in phase. After 28 days of the placebo run-in, 291 subjects (87%) met the minimum compliance rate (≥ 80%) and were randomized to continue with blinded study treatment between September 1998 and July 2000. The mean age at enrollment was 60.9 years, with a median of 61.9 years. Among randomized subjects 175 (60%) were male and 116 (40%) were female. For performance status, most randomized subjects (267, or 92%) were level 0 at enrollment, with 23 subjects at level 1 and one at level 2. Nearly all subjects (290, or 99.7%) were white, non-Hispanic with one Hispanic subject.
Baseline characteristics are summarized in . Body surface area, which was derived from height and weight, was used to determine the dose of study medication. The resulting mean and median values for randomized subjects were both 1.96 m2. Baseline variables across the two treatment groups appeared reasonably well balanced and consistent with randomization, with the possible exception of weight (Wilcoxon p-value=0.060) and body surface area (Wilcoxon p-value=0.063). At each study visit, subjects were asked if they had used any of five specific medications since their prior visit: sunscreen, vitamin A, vitamin C, vitamin E, or any non-steroidal anti-inflammatory drug (NSAID). The observed differences in baseline concomitant medication use between treatment groups were small and appeared to be consistent with randomization.
Randomized Subject Baseline Characteristics
presents information on skin cancer history, the number of prior skin cancers, and the time from the subject’s first skin cancer diagnosis to study enrollment. Time since first diagnosis was summarized in 6-month intervals, with showing the percent of subjects falling within each interval. Most subjects (208, or 71%) reported fewer than five prior skin cancers; and 16 subjects (5%) had 15 or more prior skin cancers. The mean number of prior cancers among randomized subjects was 4.5, with a median of 2; values ranged from 1 prior skin cancer to 74. Although somewhat unbalanced between the treatment groups, a mean of 4.23 prior skin cancers occurred in subjects randomized to DFMO as compared to a mean of 4.91 among placebo subjects. A Wilcoxon rank-sum test comparing the distribution among randomized subjects in the two groups did not achieve statistical significance (p-value of 0.10). Time since first diagnosis differed slightly between groups: more subjects randomized to placebo had a first diagnosis more than 24 months prior to enrollment (69% vs. 51%), while more subjects on DFMO had their first diagnosis within the previous six months. The p-value from a Wilcoxon test of the distribution of ordered time categories between groups was 0.002. Consistent with the longer history of skin cancers in the placebo group the skin cancer rate () was slightly higher in the DFMO group.
1a – Number of prior skin cancers per subject; 1b – Duration in months from first skin cancer to study enrollment. The difference between the groups was assessed using the Wilcoxon rank- sum test.
Of the 291 subjects randomized to study treatment, 168 subjects completed four years of study drug treatment and 6 months of follow-up after stopping study drug. One hundred twenty-three subjects (42% of randomized subjects) discontinued study drug treatment early (90 subjects stopped secondary to adverse events and 21 withdrew consent). However, many of those who discontinued were evaluated for follow-up status and new skin cancers after stopping treatment. When the trial ended, there were a total of 1,202 observed person-years of follow-up for all randomized subjects. There was a mean follow-up time of 4.1 years per subject (median 4.5 years) and a maximum of 5.3 years.
The primary endpoint of the study was the number of new NMSC events observed between subjects randomized to DFMO or placebo. summarizes the NMSC events and graphs the probability of developing a NMSC. Over the course of approximately 1200 subject-years of follow-up 623 new NMSC observed, 260 in the DFMO group, with an event rate of 0.44 cancers per year of follow-up, and 363 in the placebo group, for an event rate of 0.61 (two sample t test comparing cancer incidence rates, p = 0.069). The number of NMSC per subject ranged from 0–33 with an event-rate of 0.5 NMSC’s per subject-year. Consistent with the expected pattern for NMSC in immune-competent patients, basal cell cancers were predominant. Examining the subsets of basal cell and squamous cell cancers the majority of difference in NMSC events between the two groups was within the basal cell cancer category (see ). Subjects receiving DFMO had a significantly lower (p=0.03) rate of basal cell cancers per year of follow-up than subjects on placebo (0.28 vs. 0.40). This significant difference was maintained when controlling for differences in prior skin cancer history between the groups.
Figure 2 2a – Probability of remaining recurrence free over time as indicated by the Kaplan-Meier estimator. Time to first non-melanoma skin cancer (NMSC) in study. Time to first diagnosis was computed from the date of first new skin cancer diagnosis after (more ...)
show the results of TPA-induced ODC activity and putrescine, spermidine and spermine levels from normal skin at baseline and again 24, 36 and 48 months after starting study drug treatment. Subjects receiving DFMO had a significant (p<0.001) reduction in TPA-induced skin ODC activity throughout study participation. Skin putrescine concentrations were significantly lower in subjects on DFMO at 24 and 36 months but not at 48 months. Despite a trend toward lower skin spermidine concentrations in subjects randomized to DFMO at month 24 (p=0.06) and significantly lower concentrations at month 36 (p<0.001), there was no difference at month 48. There was no apparent difference in skin spermine concentrations at any time point. When comparing the above parameters across treatment groups only in the subset of subjects with or without recurrence of NMSC, the same presence or absence of a significant difference between treatment groups was observed.
Figure 3 Skin Biomarkers Box Plots. Median values , boxes denote first (lower border) and third (upper border) quartiles of the data distribution, and lines/whiskers denote 5th (lower) and 95th (upper) percentile of the distribution. The differences (more ...)
Compliance with study drug was excellent throughout the study. Overall compliance (expressed as percent of days taking the study drug as instructed) was 91.9±14.5% (mean±S.D.) or a median of 98.4% for the DFMO group and 93.5±11.6% or a median of 98.3% for the placebo group. The compliance was nearly identical when comparing the liquid formulation versus pills. The liquid formulation (DFMO or placebo) was taken by 271 patients for a median time of 1.56 years. The tablet formulation (DFMO or placebo) was taken by 207 patients for a median time of 2.53 years.
Adverse events during the placebo run-in phase (28 days) were uncommon except for gastrointestinal toxicity, which was reported by 20% of participants and primarily consisted of grade 1 nausea or diarrhea. After randomization, adverse events were common throughout the study with 95% of subjects in each group reporting at least one. compare the DFMO and placebo groups relative to general toxicity events and the most common specific adverse events, respectively. Gastrointestinal adverse events were the most commonly observed toxicity, and nausea or diarrhea were often attributed as possibly related to study drug. As shown in , gastrointestinal pain was more commonly observed in the placebo group. With regard to serious adverse events (i.e., hospitalizations, surgeries, grade 3 or 4 toxicities), 36 occurred in DFMO subjects and 35 in placebo subjects. Among these 71 events, 20 of the 36 subjects with grade 4 or life-threatening events had been randomized to DFMO. Ten subjects/events were attributed as probably related with 26 events described as possibly or unlikely related to study drug. Attribution descriptions (definitely, probably, possibly, unlikely or not related) were the same for both groups. The timing of serious or not serious adverse events was evaluated, and there were no differences in time-to-event or freedom-from events between the DFMO or placebo groups. Greater than or equal to grade 2 adverse events required study drug discontinuation, which occurred in approximately 30% (90 subjects) of randomized subjects, Despite the lack of any obvious differences in adverse events or rate between the two groups, significantly more subjects taking DFMO (36%) (p=0.058) had to discontinue study treatment due to ≥ grade 2 adverse event than subjects taking placebo (26%) (). This was predominately due to the increased rate of grade 2 audiometric abnormalities in subjects taking DFMO.
Figure 4 Adverse events after randomization. The differences between the groups were assessed using chi-square tests. 4a – Overview of Adverse Events after randomization. 4b – Incidence of specific, more common toxicities by treatment group and (more ...)
An audiogram was performed before beginning study treatment to assess baseline hearing status; of the 289/291 randomized subjects who had audiogram results recorded from that visit, 190 (66%) were reported as having normal hearing and 99 (34%) as abnormal. 244 subjects had an audiogram after one year on study. While there was no difference between groups in self-reported hearing loss or tinnitus, the audiograms reveal significant differences between the groups. While the overall average decibel loss at one year was approximately 1 dB in the DFMO group and zero in the placebo group, this was statistically significant (p=0.0001). Greater ototoxicity (resulting in study drug discontinuation) was found in the DFMO group as measured by the proportion of subjects with ≥ 15 dB hearing loss at 2 adjacent frequencies, but this did not achieve statistical significance (10.8% in the DFMO group and 4.5% in the placebo group, p=0.06). At the end of study () the overall average hearing loss was significantly greater in the DFMO arm (p=0.003) with approximately 4 dB of loss in the DFMO group and 2 dB of loss in the placebo group. When comparing proportions of subjects with potentially significant hearing changes, the differences were not significant but trended toward a greater proportion in the DFMO group, 45.2% of DFMO subjects versus 33.6% of placebo subjects had ≥ 15 dB hearing loss at 2 adjacent frequencies (p=0.07). Whenever feasible, subjects with significant hearing changes on audiogram underwent repeat audiograms 6 months later to assess reversibility. Thirty-one (19%) DFMO subjects and 33 (18%) placebo subjects had persistent abnormalities 6 months after stopping study drug. No additional audiometric testing was done.
End of Study Audiometry results by treatment group. The panel summarizes the worst change for each subject according to certain thresholds. The differences between the groups were assessed using the Wilcoxon rank-sum test.
Twelve study subjects died during study participation or follow-up, 7 on the DFMO arm (age 69 to 78 y.o.) and 5 on the placebo arm (age 62 to 78 y.o.). While no deaths were felt to be possibly or probably related to the study drug 4 deaths on the DFMO arm are described: (1) a 69 y.o. took drug for 18 months and stopped due to cardiac disease and died 6 months later from congestive heart failure; (2) a 70 y.o. on drug for 30 months died 10 days after the last dose with a ruptured spleen and congestive heart failure; (3) a 69 y.o. took drug for 12 months and died 2 months later related to a cerebrovascular accident; and (4) a 76 y.o. took drug for 24 months and died from acute renal failure 4 months later.