The outlook in gastric cancer is dominated by how far the cancer has spread at diagnosis. Depth of invasion and nodal involvement together predict outcome more strongly than any single molecular finding, and the reason stage matters so much is that early disease can be cured by surgery while metastatic disease generally cannot.
What stage means for survival
In the United States, the overall 5-year relative survival for stomach cancer is about 40%. The figure is built from very different groups. When the cancer is localised, confined to the stomach, 5-year survival is about 78%; when it has spread to regional lymph nodes it is about 39%; and when it has metastasised it is about 8%. Only about a third of patients are diagnosed at the localised stage, which is why the overall figure sits far below the localised one.
Early gastric cancer, confined to the mucosa or submucosa, has a much better prognosis still, with reported 5-year survival above 90% in series from the Far East, where it is diagnosed far more often.
Tumour factors that shift the outlook
Where the tumour sits in the stomach changes the outlook. Cancers of the distal stomach do better than tumours of the proximal stomach and cardia; more than half of patients with localised distal gastric cancer can be cured, whereas the 5-year survival of proximal gastric cancer is only 10 to 15%.
The histological and molecular type shifts it further. Diffuse-type tumours, which infiltrate the wall as linitis plastica, do worse than intestinal-type tumours. Among the molecular subtypes, microsatellite-unstable tumours have the best outcome and genomically stable and mesenchymal tumours the worst, and decreased expression of the cell-cycle protein p27 is a marker of poor prognosis. Taken together, the extent of the tumour and its nodal involvement remain the strongest predictors, with these biological features refining the estimate.