Viral pneumonia in a patient treated with pembrolizumab - similarity with immune-related pneumonitis.

Background: Immunotherapy is one of the fundamental treatment modalities, especially in the treatment of metastatic non-small cell lung carcinoma, but it is also applied in neoadjuvant, or adjuvant therapy. A certain limitation continues to be immune-mediated toxicity and the broad clinical spectrum of its manifestations, which can present considerable differential diagnostic challenges.

Case: We present a case of a female patient who has been treated at our institute since February 2023 for metastatic squamous cell carcinoma of the right lung with first-line systemic therapy of pembrolizumab in initial combination with carboplatin and paclitaxel. Reassessment after four cycles of treatment showed a significant regression of the oncological finding, but also partial fibrotic changes in both lungs. The patient was completely asymptomatic and after consultation with her, it was decided to continue the treatment, now with pembrolizumab monotherapy. Several days after administration, the patient developed resting dyspnea, cough, and fevers. She consulted this deterioration of her condition only at the next scheduled appointment. Persistent dyspnea raised suspicion of immune-mediated pneumonitis. CT of the chest showed significant involvement of all lung lobes and treatment with corticosteroids and antibiotics was initiated. Through bronchoalveolar lavage, positivity for rhinovirus and enterovirus was detected. Viral pneumonia was assessed as the most likely cause of the clinical finding. The established corticosteroid treatment was gradually reduced and after discussion with the patient, we continued the administration of pembrolizumab. A follow-up CT of the lungs showed both further significant regression of the tumor and significant regression of inflammatory changes. Currently, the patient is after a total of 14 cycles of chemo/immunotherapy (of which 9 cycles of pembrolizumab after re-initiation), clinically in excellent condition, while a significant therapeutic response continues.

Conclusion: Our case report emphasizes the need for a broader differential diagnosis in the event of pulmonary complications during the administration of immunotherapy. Correct diagnosis of these complications can, among other things, fundamentally affect oncological treatment.