Low-Shot Prompt Tuning for Multiple Instance Learning Based Histology Classification

In recent years, prompting pre-trained visual-language (VL) models has shown excellent generalization to various downstream tasks in both natural and medical images. However, VL models are sensitive to the choice of input text prompts, requiring careful selection of templates. Moreover, prompt tuning in the weakly supervised/multiple-instance (MIL) setting is fairly under-explored, especially in the field of computational pathology. In this work, we present a novel prompt tuning framework leveraging frozen VL encoders with (i) residual visual feature adaptation, and (ii) text-based context prompt optimization for whole slide image (WSI) level tasks i.e., classification. In contrast with existing approaches using variants of attention-based instance pooling for slide-level representations, we propose synergistic prompt-based pooling of multiple instances as the weighted sum of learnable-context and slide features. By leveraging the mean learned-prompt vectors and pooled slide features, our design facilitates different slide-level tasks. Extensive experiments on public WSI benchmark datasets reveal significant gains over existing prompting methods, including standard baseline multiple instance learners.