A Mycobacterial Masquerade: A Case of Tuberculosis in a Patient With Suspected Lung Cancer Progression

Abstract Lung cancer and mycobacterium tuberculosis (MTB) infection have a strong association worldwide. Infections such as MTB should be suspected in cancer patients when imaging demonstrates atypical lesions or discordant responses to treatment.A 79-year-old male prior smoker from the Philippines presented to the Pulmonary clinic with a right lower lobe mass and was diagnosed with Stage IV (T3N2M1) lung adenocarcinoma with metastatic brain lesions. He was prescribed Osimertinib after driver mutation testing identified an EGFR exon 19 deletion mutation. After three months of Osimertinib, there was reduction in size of both his lung mass and his brain metastases, although he was noted to have micronodularity in his left upper lobe. This progressed to several coalesced nodules on subsequent surveillance imaging. A PET-CT was obtained 18 months following diagnosis of cancer, which demonstrated avidity of the left upper lobe nodules and a mediastinal lymph node. The lower lobe mass was diminished in size and avidity. He underwent EBUS-TBNA of the lymph node and radial probe biopsy of the nodularity. Bronchioalveolar lavage demonstrated a lymphocyte predominance. Respiratory culture and acid-fast smear were negative and cytology demonstrated no evidence of malignancy. Five weeks following the procedure, acid fast culture grew MTB. The patient was subsequently started on RIPE therapy. Due to the known interaction with rifampin, his Osimertinib dose was doubled for the duration of his treatment course. He has tolerated this treatment well and he will undergo repeat imaging following completion of antibiotics.There is a known association between lung cancer and MTB, and in areas with a high prevalence, this infection is an independent risk factor for the development of lung cancer, likely due to chronic inflammation. Many cancer treatments, particularly chemotherapy and immune checkpoint inhibitors, predispose patients with latent tuberculosis to activation. Tyrosine kinase inhibitors (TKIs) targeting EGFR mutations, as used here, do not impact immunity, and are not associated with increased risk of active MTB infection. This patient was diagnosed with tuberculosis after his surveillance imaging was suspicious for lesions responding discordantly from known cancer. This highlights the importance of screening patients with risk factors for MTB when diagnosed with lung cancer. Having a low threshold to repeat biopsy in patients with incomplete or discordant responses to cancer treatment can help to avoid delayed treatment and community exposure.