Actinomycosis Mimicking Invasive Colon Cancer with Multiorgan Involvement: A Case Report

Abdominal actinomycosis is a rare chronic infection caused by Actinomyces species that often mimics advanced intra-abdominal malignancies, making early diagnosis difficult.We report the case of an 82-year-old woman who presented with intermittent left abdominal pain and a palpable mass.Imaging revealed a large pericolic mass with suspected invasion of the stomach and abdominal wall, raising strong suspicion for colon cancer with regional lymph node involvement and possible peritoneal carcinomatosis.Core needle biopsy results suggested an inflammatory myofibroblastic tumor.Because malignancy could not be ruled out, surgical resection-comprising extended left hemicolectomy, gastric wedge resection, and abdominal wall excision-was performed.Histopathological examination demonstrated multiple abscesses containing gram-positive bacilli, consistent with actinomycosis.The patient received high-dose intravenous penicillin followed by prolonged oral therapy and remained symptomfree at the 1-year follow-up.This case underscores the diagnostic challenge of abdominopelvic actinomycosis, particularly when it involves multiple organs and radiologically mimics invasive malignancy.Clinicians should consider this rare entity in the differential diagnosis of tumorlike abdominal lesions, especially when radiologic or endoscopic findings are atypical, to avoid unnecessary aggressive interventions and ensure appropriate management.