Step 1: Evaluate each statement about gastric lymphoma in turn. The stomach is the leading extranodal lymphoma site, and the dominant histology is MALT lymphoma, which is a non-Hodgkin B-cell lymphoma - so the commonest variety being NHL is accurate.
Step 2: A strong, direct link with Helicobacter pylori exists; the majority of MALTomas arise on a background of H. pylori gastritis, and antibiotic eradication can produce lasting remission, proving the connection.
Step 3: The tissue diagnosis is confirmed by endoscopic biopsy, making the biopsy statement true as well.
Step 4: With every individual statement valid, the inclusive option covering all of them is correct.
\[\boxed{\text{All of the above}}\]