The correct answer is the third option; T stage is best assessed by EUS. The T stage of luminal gastrointestinal malignancies depends upon the depth of invasion of the tumor into the gastric wall (T1: tumor invades the lamina propria/muscularis mucosae (T1a) or the submucosa (T1b); T2: invades the muscularis propria; T3: tumor invades the subserosal connective tissue; T4: tumor invades the serosa (T4a) or the adjacent structures (T4b). While cross-sectional imaging (CT and MRI) can readily identify metastatic disease or high T stage tumors that invade other organs, its spacial resolution does not allow for accurate estimation of tumor wall invasion. Endoscopic ultrasound, with its close proximity to the gastrointestinal (GI) lumen, allows for more accurate estimation of tumor invasion. The muscularis propria, an important landmark for GI luminal T staging, is especially visible on EUS, and can allow for more accurate differentiation of T2 and T3 lesions (as well as deeper invasion). Differentiating early stage GI tumors (T1a and T1b) is more difficult and generally relies on pathologic staging (via surgery or endoscopic mucosal resection). EUS can also identify and allow for fine needle aspiration of regional lymph nodes.
Gastric carcinomas are biologically heterogeneous with multifactorial environmental and/ or genetic etiologies. Risk factors more likely associated with intestinal-type gastric cancers include smoking, diets high in salt-preserved and/or smoked food, bile reflux in the context of Billroth resections, autoimmune gastritis and infection with H. pylori. Approximately 1–3% of gastric cancers are truly hereditary. Diffuse or poorly cohesive type gastric carcinomas in patients younger than 30 years old are more likely to be genetically determined, related to deficiency of E-cadherin synthesis. Gastric cancer predisposition has been also linked to other cancer syndromes, including Lynch syndrome (LS), Peutz-Jeghers syndrome (PJS), Li-Fraumeni syndrome, familial adenomatous polyposis syndrome (FAP), and gastric adenocarcinoma and proximal polyposis syndrome of the stomach. Similar to sporadic gastric cancer, gastric cancer in these syndromic patients can be either intestinal or diffuse type.