Zahrieh, David

Background/Objectives. Decades of research have failed to uncover effective approaches to prevent chemotherapy-induced peripheral neuropathy (CIPN), a common side effect of neurotoxic chemotherapy. Increased interest in placebo response as a potentially under-recognized confounder in CIPN trials was recently sparked by the results of a multisite NCI-funded phase II-III CIPN prevention study of duloxetine, a promising serotonin–norepinephrine reuptake inhibitor that enhances pain-inhibitory mechanisms within the central nervous system. Study findings revealed high and nearly equivalent response rates in three randomized treatment groups—little to no CIPN was reported by 65.2%, 66.0%, and 68.0% of study participants who received duloxetine 30 mg, 60 mg, or placebo treatment, respectively. Methods. We performed a meta-analysis of placebo response rates from seven randomized, double-blinded, placebo-controlled trials conducted over the past 20 years and comprising 191 placebo participants that were specifically testing interventions for oxaliplatin- and paclitaxel-induced peripheral neuropathy and that serially collected patient responses on the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire for Chemotherapy-Induced Neuropathy questionnaire. Additionally, we sought to identify trial- and patient-specific factors that predicted higher placebo response rates from a participant-level pooled analysis. Results. The placebo response rate was 10.0% [95% CI: 5.8%, 16.6%] when response was defined more conservatively as patients reporting no neuropathy at all. When the placebo response was defined more broadly based on patients reporting no or a little neuropathy, the placebo response rate was higher (39.6% [95% CI: 27.4%, 53.2%]). Male participants, receipt of oxaliplatin, and a 2:1 randomization ratio favoring the intervention arm were individually associated with a higher placebo response. Conclusions. High placebo response rates can threaten scientific progress toward identifying effective treatments for cancer treatment-associated side effects, like CIPN. Careful attention to study design factors, participant eligibility, and patient and research staff expectations may help to minimize placebo response rates in future CIPN intervention studies.

PURPOSE The primary objective of this randomized, double-blind, placebo-controlled, multicenter phase II study (Alliance A221805) was to screen two doses of duloxetine for preventing sensory oxaliplatin-induced peripheral neuropathy (OIPN). METHODS Participants were randomly assigned 1:1:1 to receive once daily 30 mg duloxetine, 60 mg duloxetine, or placebo. Eligible participants had stage II to III colorectal cancer and no baseline neuropathy, had Eastern Cooperative Oncology Group performance status 0-2, were age 25 years and older, and received oxaliplatin via one of the following doses and schedules: 85 mg/m 2 every 2 weeks (6 or 12 doses) or 130 mg/m 2 every 3 weeks (4 doses). Duloxetine/placebo was taken once daily beginning day 1 of cycle 1 and continued for 17 weeks. The primary end point, a composite response reflecting sensory OIPN symptom severity and onset, was measured in weeks 19-21 using a validated participant-reported outcome survey assessing extremity numbness, tingling, and pain. Response was defined as a participant-reported highest score of ≤2 (ie, 1 = not at all; 2 = a little) on survey items. To be evaluable for the response end point, eligible participants must have initiated oxaliplatin and submitted ≥1 postbaseline OIPN survey. RESULTS Of the 199 participants (n = 66, 30 mg duloxetine; n = 66, 60 mg duloxetine; n = 67, placebo), 46, 47, and 50 (N = 143, 71.8%), respectively, were evaluable for primary end point analysis based on modified intention-to-treat criteria. Participant mean age was 55.1 years (standard deviation = 10.4). Most were White (n = 113, 80.7%) and male (n = 82, 58.6%). The proportion of responders among those receiving placebo (68.0%) was similar to those receiving duloxetine 30 mg (65.2%) or 60 mg (66.0%). Duloxetine adherence rates, measured via pill counts—30 mg (54%), 60 mg (57%), and placebo (59%) groups—were low (<75%). CONCLUSION Duloxetine is not more promising than placebo for preventing sensory OIPN.