  Gastric cancer is the third leading cause of cancer-related mortality
worldwide, but no guideline-recommended screening test exists. Existing methods
can be invasive, expensive, and lack sensitivity to identify early-stage
gastric cancer. In this study, we explore the feasibility of using a deep
learning approach on non-contrast CT scans for gastric cancer detection. We
propose a novel cluster-induced Mask Transformer that jointly segments the
tumor and classifies abnormality in a multi-task manner. Our model incorporates
learnable clusters that encode the texture and shape prototypes of gastric
cancer, utilizing self- and cross-attention to interact with convolutional
features. In our experiments, the proposed method achieves a sensitivity of
85.0% and specificity of 92.6% for detecting gastric tumors on a hold-out test
set consisting of 100 patients with cancer and 148 normal. In comparison, two
radiologists have an average sensitivity of 73.5% and specificity of 84.3%. We
also obtain a specificity of 97.7% on an external test set with 903 normal
cases. Our approach performs comparably to established state-of-the-art gastric
cancer screening tools like blood testing and endoscopy, while also being more
sensitive in detecting early-stage cancer. This demonstrates the potential of
our approach as a novel, non-invasive, low-cost, and accurate method for
opportunistic gastric cancer screening.
