Peritoneal Tuberculosis Mimicking Cancerous Peritonitis With Elevated Serum Cancer Antigen 125 and Carbohydrate Antigen 19‐9 Levels: A Case Report

Peritoneal tuberculosis (PTB) is a rare extrapulmonary manifestation that poses diagnostic challenges due to nonspecific clinical features and can mimic carcinomatous peritonitis, particularly in patients with ascites and elevated serum cancer antigen 125 (CA125) and carbohydrate antigen 19-9 (CA19-9) levels. We report a 75-year-old woman with rheumatoid arthritis who was receiving certolizumab and developed massive ascites, elevated tumour markers, and pulmonary nodules. Laparoscopy revealed numerous miliary yellow-white nodules in the parietal peritoneum, and biopsy showed epithelioid granulomas with positive Ziehl-Neelsen staining. Sputum acid-fast bacilli culture and PCR for <i>Mycobacterium tuberculosis</i> were both positive, leading to the diagnosis of pulmonary and peritoneal tuberculosis. After antituberculous therapy, CA125 and CA19-9 levels decreased markedly. While CA19-9 is generally considered a marker for malignancy, it may increase in cases of tuberculosis and bronchiectasis. PTB should be considered in the differential diagnosis even when carcinomatous peritonitis is strongly suspected.