Anti-programmed death 1 antibody in the treatment of coexistent Mycobacterium fortuitum and lung cancer: A case report

BACKGROUND: Nontuberculous mycobacterium (NTM) refers to all mycobacteria except Mycobacterium tuberculosis and Mycobacterium leprae, also known as environmental Mycobacterium. The patients with lung cancer and NTM are somewhat special; the two diseases are inevitably influenced by each other. It brings difficulties and challenges to the choice of treatment. Recently, cancer immunotherapy has been considered one of the pillars for the treatment of lung cancer. However, the clinical experience in the application of immune checkpoint inhibitors is scarce for lung cancer patients with pulmonary tuberculosis, and lung cancer with NTM is even more rare. Although it ameliorates lung cancer, immunotherapy with immune checkpoint inhibitors presents complications of infectious diseases, including tuberculosis and NTM. CASE SUMMARY: A 61-year-old male patient visited a doctor in May 2019. His admitting diagnoses were: (1) Cancer of the left lung with a pathological diagnosis of poorly differentiated non-small cell carcinoma, likely poorly differentiated adenocarcinoma, clinical stage IIIb (T3N3M0); and (2) Mycobacterium fortuitum (M. fortuitum) infection. We chose to proceed with pembrolizumab treatment. After two treatment cycles, a chest computed tomography scan showed a new irregular subpleural mass in the anterior segment of the left upper lobe of the lung, a reduction in the mediastinal enlarged lymph node, and no other obvious changes. Next, an ultrasound-guided biopsy of the new tumor was performed. Pathological examination showed that a large number of carbon particles were deposited in the alveolar tissue with histiocyte reaction and multinucleated giant cell formation. The tuberculosis (TB) specialist suggested that anti-TB therapy be combined with continued antitumor treatment. The patient continued to be treated with pembrolizumab. After 14 cycles, the lesion shrunk by 79%, there was no recurrence of M. fortuitum infection, and there were no intolerable adverse reactions. CONCLUSION: We have observed that in cases of lung cancer complicated with M. fortuitum infection, opportunistic pathogen infection recurrence can be overcome, and immunotherapy is most beneficial when TB doctors and oncologists cooperate to closely observe dynamic changes in M. fortuitum and lung cancer. Treatment should be maintained with low dosage anti-TB drugs after general anti-TB chemotherapy for 1 year; this may prevent opportunistic pathogen infection recurrence during immunotherapy.