[Paper Review] Multi-Task Learning for Post-transplant Cause of Death Analysis: A Case Study on Liver Transplant

Sirui Ding, Qiaoyu Tan+6 more|PubMed|Mar 30, 2023

Machine Learning in Healthcare28 references8 citations

TL;DR

The paper introduces CoD-MTL, a tree-distillation multi-task learning framework that jointly predicts post-transplant causes of death (rejection and infection) in liver transplant patients, improving accuracy over traditional models and single-task baselines.

ABSTRACT

Organ transplant is the essential treatment method for some end-stage diseases, such as liver failure. Analyzing the post-transplant cause of death (CoD) after organ transplant provides a powerful tool for clinical decision making, including personalized treatment and organ allocation. However, traditional methods like Model for End-stage Liver Disease (MELD) score and conventional machine learning (ML) methods are limited in CoD analysis due to two major data and model-related challenges. To address this, we propose a novel framework called CoD-MTL leveraging multi-task learning to model the semantic relationships between various CoD prediction tasks jointly. Specifically, we develop a novel tree distillation strategy for multi-task learning, which combines the strength of both the tree model and multi-task learning. Experimental results are presented to show the precise and reliable CoD predictions of our framework. A case study is conducted to demonstrate the clinical importance of our method in the liver transplant.

Motivation & Objective

• Motivate accurate post-transplant cause-of-death analysis to aid organ allocation and personalized treatment.
• Address data imbalance and task correlation by using a multitask framework for related CoD prediction tasks.
• Leverage a tree-distillation strategy to transfer tree-model strengths into neural networks for multi-task learning on EHR data.
• Evaluate the method on a real liver transplant cohort to demonstrate clinical relevance and predictive performance.

Proposed method

• Preprocess EHR features by encoding categorical data, concatenating with numerical features, and imputing missing values with zeros.
• Develop a multi-task learning framework (CoD-MTL) with a shared representation and task-specific heads for multiple CoD tasks (rejection and infection).
• Introduce a tree-distillation strategy that distills outputs from GBDT models into a neural network via dense embeddings of tree leaves, enabling end-to-end multi-task learning.
• Train task-specific distilled networks NN_j with a shared representation for all CoD tasks and combine them with a multi-task loss that balances distillation and prediction terms.
• Integrate distillation targets from per-task GBDT models into a unified multi-task neural architecture to improve performance on tabular EHR data.

Experimental results

Research questions

• RQ1 RQ1: Can CoD-MTL accurately predict rejection and infection as post-transplant CoDs?
• RQ2 RQ2: Is the CoD-MTL model trustworthy with well-calibrated probability estimates and stable performance?
• RQ3 RQ3: How can CoD-MTL support clinical decision-making in liver transplantation?

Key findings

• CoD-MTL achieves higher AUROC and AUPRC than all baselines for both rejection and infection predictions.
• Tree-based models outperform single-task neural nets, and multitask learning further improves performance over single-task baselines.
• CoD-MTL shows up to 16.1% AUROC improvement for rejection and 15.6% AUROC improvement for infection over best baselines; similar gains are seen in AUPRC.
• Calibration analyses indicate CoD-MTL probabilities are well-calibrated with low uncertainty across cross-validation folds.
• Case study illustrations suggest the model can provide nuanced, patient-specific risk profiles to aid clinical decisions.
• Limitations discussed include interpretability and fairness, with future work aiming to address explainable AI and equity constraints.