Abstract 1334P
Background
Solid tumors may occasionally regress even without treatment, either spontaneously or as a result of placebo effect. Such spontaneous regressions or responses are intriguing from both scientific and regulatory standpoints. We conducted an updated systematic review and meta-analysis of clinical trials of anticancer drugs in advanced solid tumors to estimate an updated placebo response rate in the targeted therapy/immunotherapy era.
Methods
Meta-analysis of placebo-controlled RCTs of anticancer drugs for advanced solid tumors published during 2015-2019. Included RCTs: (1) assessed advanced adult solid tumours only; (2) not neo/adjuvant therapy; (3) not local therapies such as surgery or radiation, cell-based therapies, or supportive care; (4) had a sample size greater than 20 participants; (5) randomly allocated patients to either treatment or placebo arms; (6) the placebo arm was a monotherapy or was used in combination with the best supportive care; (7) was not a duplicate trial or subgroup analysis; (8) measured objective response rates as outlined by the Response Evaluation Criteria in Solid Tumours (RECIST). Primary endpoint was to estimate a summary objective response rate of placebo in anti-cancer clinical trials.
Results
31 phase 3 RCTs including 4887 patients on placebo met our inclusion criteria and formed the study cohort. The pooled overall ORR, CR and PR rates in the placebo arm, using random-effects model, were 2% (95% CI, 1% to 3%), 0.01% (95% CI, 0% to 0.15%), and 2% (95% CI, 1% to 4%) respectively. Higher placebo responses were observed in maintenance therapy trials and prostate cancer trials.
Conclusions
Overall, 2% patients with advanced solid tumors can expect to achieve some response even in absence of treatment. However, complete regression without treatment is rare. This data can help clinical and regulatory policy.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
B. Gyawali: Financial Interests, Personal, Invited Speaker, For writing Medscape Columns: Medscape; Financial Interests, Personal, Invited Speaker, For giving invited talks and grand rounds at universities, cancer centers and professional societies: Various academic and professional organizations; Financial Interests, Personal, Other, Consulting services: Vivio Health; Non-Financial Interests, Member: ASCO, IASLC, JSMO. All other authors have declared no conflicts of interest.