A derived prognostic model failed external cross-platform validation, a phenomenon driven by the reversal of risk effects for <i>FABP4</i> and other genes across different populations.<h4>Conclusions</h4>This study uncovers two distinct metabolic-immune subtypes of GC and demonstrates that the prognostic effect of <i>FABP4</i> is not fixed but is highly dependent on its cellular source and the tumor microenvironmental context. Here, FABP4 is linked to neoplasm.