A 58-year-old man from rural India presents with a 4-month history of progressive dysphagia, early satiety, and unintentional weight loss of 8 kg. Upper endoscopy reveals a large ulcerated lesion in the gastric antrum. Biopsies confirm adenocarcinoma. CT chest and abdomen shows no distant metastases, but there is involvement of the perigastric lymph nodes. What is the most appropriate next step in management?