Mixture survival models methodology: an application to cancer immunotherapy assessment in clinical trials

TL;DR

This paper presents a five-step methodology for applying mixture survival models to analyze long-term survivors in cancer immunotherapy clinical trials, demonstrating its effectiveness with lung cancer data.

Contribution

It introduces a novel five-step approach for using mixture parametric models to assess immunotherapy effectiveness, accounting for population heterogeneity.

Findings

Mixture models identified 44% long survivors in vaccinated patients.

Significant differences in survival were found between treatment groups in both subpopulations.

The methodology improved detection of immunotherapy effects over standard models.

Abstract

Progress in immunotherapy revolutionized the treatment landscape for advanced lung cancer, raising survival expectations beyond those that were historically anticipated with this disease. In the present study, we describe the methods for the adjustment of mixture parametric models of two populations for survival analysis in the presence of long survivors. A methodology is proposed in several five steps: first, it is proposed to use the multimodality test to decide the number of subpopulations to be considered in the model, second to adjust simple parametric survival models and mixture distribution models, to estimate the parameters and to select the best model fitted the data, finally, to test the hypotheses to compare the effectiveness of immunotherapies in the context of randomized clinical trials. The methodology is illustrated with data from a clinical trial that evaluates the effectiveness of the therapeutic vaccine CIMAvaxEGF vs the best supportive care for the treatment of advanced lung cancer. The mixture survival model allows estimating the presence of a subpopulation of long survivors that is 44% for vaccinated patients. The differences between the treated and control group were significant in both subpopulations (population of short-term survival: p = 0.001, the population of long-term survival: p = 0.0002). For cancer therapies, where a proportion of patients achieves long-term control of the disease, the heterogeneity of the population must be taken into account. Mixture parametric models may be more suitable to detect the effectiveness of immunotherapies compared to standard models.