ELM: Ensemble of Language Models for Predicting Tumor Group from Pathology Reports

Abstract

Population-based cancer registries (PBCRs) face a significant bottleneck in manually extracting data from unstructured pathology reports, a process crucial for tasks like tumor group assignment, which can consume 900 person-hours for approximately 100,000 reports. To address this, we introduce ELM (Ensemble of Language Models), a novel ensemble-based approach leveraging both small language models (SLMs) and large language models (LLMs). ELM utilizes six fine-tuned SLMs, where three SLMs use the top part of the pathology report and three SLMs use the bottom part. This is done to maximize report coverage. ELM requires five-out-of-six agreement for a tumor group classification. Disagreements are arbitrated by an LLM with a carefully curated prompt. Our evaluation across nineteen tumor groups demonstrates ELM achieves an average precision and recall of 0.94, outperforming single-model and ensemble-without-LLM approaches. Deployed at the British Columbia Cancer Registry, ELM demonstrates how LLMs can be successfully applied in a PBCR setting to achieve state-of-the-art results and significantly enhance operational efficiencies, saving hundreds of person-hours annually.