Microscopic and immunohistochemical study findings of the patient's gastric MALT lymphoma in the past 2 years. (A) Gastric glands infiltrated by small monotonous lymphocytic cells (H&E, ×200). (B, C) Notable lymphoepithelial lesions demonstrated by the immunohistochemical stain for cytokeratin. (D) Neoplastic B-cells' low proliferative nature demonstrated by the Ki-67 labeling index. Gross and microscopic findings of the palatine tonsils. (E) Enlarged bilateral palatine tonsils covered with purulent exudate and showing shallow ulcer. (F) Low-magnification image showing diffusely effaced follicles with shallow ulcer along the surface epithelium. (G) Small- to medium-sized monotonous neoplastic cells in the nodular area showing irregular nuclei, dispersed chromatin, and inconspicuous nucleoli (H&E, ×400). (H) Low Ki-67 labeling index of neoplastic cells composing the nodular area supporting MALT lymphoma. (I) Ulcer base consisting of solid sheets of large, atypical immunoblast-like cells with many apoptotic bodies (H&E, ×100). (J) Immunoblast-like cells showing irregular nuclear contour, open chromatin, and prominent nucleoli (H&E, ×400). Immunohistochemical staining results of the large cell area. (K) Diffuse CD20-positive solid sheets of immunoblast-like cells in the ulcer base. (L) Bcl-6 positive. (M) MUM-1/IRF-4 positive. (N) High Ki-67 labeling index. (O) Striking demonstration of CD30 reactivity. (P) EBER-ISH reactivity.