A 62-year-old Indian woman undergoes subtotal gastrectomy with D2 lymphadenectomy for T2N2 gastric cancer of the antrum. Intraoperatively, the surgeon notes that the left gastroepiploic vessels are densely adherent to the tumour and cannot be separated without breaching the tumour capsule. The surgeon divides these vessels close to the stomach. Histopathology shows a 4 cm tumour with invasion into the muscularis propria, 8 involved regional lymph nodes, and negative margins (5 cm proximal, 3 cm distal). What is the most likely reason this patient will have poor long-term survival despite R0 resection?