MedRev: Reversing Negative Transfer in Medical Multi-modal Foundation Model Fine-tuning for Improved Medical Image Analysis

Medical multi-modal foundation models (MFMs) have shown strong generalization potential for smart clinical applications. However, conflicting cross-modal priors can cause them to underperform single-modal foundation models on specific downstream tasks. We define this phenomenon as “negative multi-modal transfer”, where the transfer gain of a multi-modal backbone becomes inconsistent or negative for a target modality. Through controlled experiments, we observe that (1) the extent of pretraining and (2) which layers are selected for fine-tuning substantially affect whether knowledge transfers effectively across modalities in downstream tasks. To address this, we propose MedRev, an efficient fine-tuning paradigm developed to reverse the negative transfer effect in medical foundation models. MedRev introduces a mixture-of-pre-trained experts strategy that adaptively lever-ages knowledge from different pre-trained checkpoints based on downstream data. Moreover, a dynamic layer freezing strategy is employed to decrease unnecessary updates and fine-tune those most beneficial for the target modality. Extensive experiments on downstream datasets across ten modalities demonstrate that MedRev consistently mitigates the negative transfer and increases fine-tuning performance.