The endoscopic findings of gastric MALT lymphoma are extremely diverse, making it challenging to distinguish the lymphoma from early gastric cancer or benign gastric lesions such as atrophic gastritis or erosions. In previous studies, endoscopic findings were classified into four main types, of which large ulcer was the most common (42.9%), followed by small ulcer with gastritis (28.5%), polyps (14.3%), and other atypical forms (14.3%) [10]. Japanese studies have reported the ulcer form (33.3%), multiple erosions (23.4%), scar form (12.8%), and early gastric cancer IIc form (10.6%) [11]. In a Korean study, the findings were classified into raised, ulcer infiltration, early gastric cancer IIc, subepithelial tumor, and multiple-erosion types [12]. Consequently, careful observation and multiple biopsies of suspected lesions are necessary; repeated endoscopy and biopsy are also needed in some cases [12,13]. The various endoscopic findings of MALT lymphomas are shown in Figure 1.

Histological examination of the biopsy specimens is essential for a definitive diagnosis. Lymphoepithelial lesions are characteristic features of gastric MALT lymphoma, and the scoring system proposed by Wotherspoon et al. was used for the pathological diagnosis of the latter (Table 1) [14]. Gastric MALT lymphoma can be diagnosed if the histopathological changes correspond to a score of 5. If the score is 3 or 4, the diagnosis is confirmed based on the monoclonality of B cells using polymerase chain reaction [15]. However, these findings can be observed with inflammatory changes in the gastric mucosa; for an accurate diagnosis, evaluation by an expert pathologist is necessary [16]. Therefore, if gastric MALT lymphoma is endoscopically suspected, repeated biopsy and discussion with a pathologist should be performed, even if the histological results do not indicate MALT lymphoma in the initial examination. In some cases, endoscopic mucosal resection can be performed for a definite diagnosis that cannot be diagnosed using repeated forceps biopsy [17].

Gastric MALT lymphoma is often unaccompanied by symptoms and is limited to the primary lesion for a long period even after diagnosis. Furthermore, a long time is required before an improvement can be observed after H. pylori eradication therapy; therefore, neglecting the test for staging is easy. However, approximately 10%–25% of MALT lymphomas are diagnosed at advanced stages [18,19]. Therefore, it is imperative to evaluate the extent of disease to determine the appropriate treatment method. For the staging workup of gastric MALT lymphoma, other diagnostic modalities such as abdominal and pelvic computed tomography (CT), chest CT, and endoscopic ultrasound (EUS) are recommended in addition to endoscopic examination, histological confirmation, and H. pylori evaluation [16,20]. EUS can be used to assess the depth of tumor infiltration into the gastric wall and evaluate regional lymph node involvement. This modality provides valuable information for accurate staging and can guide the development of appropriate treatment strategies. Among the various staging systems for gastric MALT lymphoma, the Lugano system is mainly used in clinical settings (Table 2) [16]. For further workup, positron emission tomography (PET), bone marrow biopsy, or t(11;18) translocation examination can be performed in selected cases. Gastric MALT lymphoma typically presents as a small, slowly progressing primary lesion, which limits the utility of PET. Therefore, routine PET scanning is not recommended for all patients with gastric MALT lymphoma and can be considered when assessing the extent of the disease, particularly when local treatments such as radiotherapy are planned [21]. The frequency of bone marrow involvement in gastric MALT lymphoma is relatively low. Although bone marrow involvement is classified as a stage IV disease according to the clinical staging system, its impact on the clinical course remains unclear. Therefore, there is an ongoing debate regarding the necessity of routine bone marrow examination in all patients, and can be considered in those with advanced-stage disease or those who do not respond to H. pylori eradication therapy [21]. Genetic alterations are observed in a subset of gastric MALT lymphomas, and the presence of the t(11;18)(q21;q21) translocation is associated with more advanced disease stages and poor response to H. pylori eradication. Although testing for genetic alterations can help predict treatment response and prognosis, its utility is limited; therefore, routine testing is not recommended for all patients [21].