Longitudinal Latent Overall Toxicity (LOTox) profiles in osteosarcoma: a new taxonomy based on latent Markov models

In cancer trials, the analysis of longitudinal toxicity data is a difficult task due to the presence of multiple adverse events with different extents of toxic burden. Models able to summarise and quantify the overall toxic risk and its evolution during cancer therapy, which deals with both the longitudinal and the categorical aspects of toxicity levels progression, are necessary, but still not well developed. In this work, a novel approach based on Latent Markov (LM) models for longitudinal toxicity data is proposed. The latent status of interest is the Latent Overall Toxicity (LOTox) condition of each patient, which affects the distribution of the observed toxic levels over treatment. By assuming the existence of a LM chain for LOTox dynamics, the new approach aims at identifying different latent states of overall toxicity burden (LOTox states). This approach investigates how patients move between latent states during chemotherapy treatment allowing for the reconstruction of personalized longitudinal LOTox profiles. This methodology has never been applied to osteosarcoma treatment and provides new insights for medical decisions in childhood cancer therapy.