Histological changes caused by intralesional injection of a streptococcal preparation into bladder cancer

OK-432, a lyophilized preparation of Streptococcus pyogenes, was cystoscopically injected into bladder cancer to destroy cancer cells and to prevent recurrences. Marked reactions occurred such as stromal edema, vascular dilation, cancer cell exfoliation, and polymorphonuclear cell infiltration, succeeded by monocyte and lymphocyte infiltration with occasional lymph follicle formation. Cancer cells were sometimes intermingled in microscopic necrotic foci. Foamy granuloma was another characteristic finding. The postoperative follow-up study showed a significantly low recurrence rate.