Background: Streptococcus gallolyticus ssp. pasteurianus is a commensal bacterium of the alimentary tract in humans and animals. This microorganism not only causes sepsis, endocarditis, and meningitis but is also associated with colorectal tumors. We report herein a rare case of S. gallolyticus ssp. pasteurianus bacteremia in a patient with concomitant colon cancer and aggressive malignant lymphoma during the neutropenic period after chemotherapy against lymphoma. Case presentation: A 79-year-old man was found to have an adenoma in the ascending colon, and endoscopic mucosal resection (EMR) was planned to remove the lesion. However, he was diagnosed with diffuse large B-cell lymphoma during the pre-operation examination. The EMR was postponed, and he received rituximab, cyclophosphamide, etoposide, vincristine, and prednisolone (R-CEOP). He had a neutropenic fever with positive blood cultures for S. gallolyticus ssp. pasteurianus during the first course of R-CEOP. He improved as soon as cefepime was administered. Bacteremia did not recur thereafter, and he underwent EMR after completing six cycles of R-CEOP. The histological diagnosis of the colon tumor was welldifferentiated adenocarcinoma in adenoma. Streptococcus gallolyticus ssp. pasteurianus was not detected in the culture of the resected tissue. Conclusion: Although there have been few reports of bloodstream infection due to S. gallolyticus ssp. pasteurianus in patients with hematological malignancies undergoing cytotoxic chemotherapy, physicians should investigate the presence of coexisting colorectal tumors when this bacterium is isolated from blood cultures.
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