Mycobacterium tuberculosis, which mainly affects the lungs but can also invade other systems, presents a diagnostic challenge when co‐existing with autoimmune disease. We report a case of 31‐year‐old Asian woman with anti‐synthetase syndrome who developed abdominal and subcutaneous lumps during treatment, along with elevated tumor markers, raising suspicion of malignancy. Pathological examination revealed M. tuberculosis infection, changing the diagnosis to multifocal extrapulmonary tuberculosis. This case highlights the need for prompt and detailed evaluations, and the importance of broad differential diagnosis.