Platinum-doublet chemotherapy followed by pembrolizumab therapy for lung cancer with lymphangitis carcinomatosa mimicking interstitial pneumonitis

Rationale: Pembrolizumab, an immune-checkpoint inhibitor (ICI), has been shown to be effective for treatment-naive patients with non–small cell lung cancer (NSCLC) and high expression of programmed death-ligand 1 (PD-L1). Therefore, treatment regimens containing pembrolizumab have become a standard therapy for these patients. However, the use of pembrolizumab is limited owing to the side effects of ICIs. Patient concerns and diagnoses: The patient was a 65-year-old man with a left lung mass surrounded by interstitial shadow. The tumor was diagnosed as adenocarcinoma, cT4N3M0, stage IIIC, and the tumor cells showed high PD-L1 expression. It was unclear whether the interstitial shadow was interstitial lung disease (ILD) or lymphangitis carcinomatosa. Interventions and outcomes: The patient received carboplatin and nab-paclitaxel, a less risky regimen for ILD, as the first-line therapy. Administration of 2 cycles of this regimen markedly improved both the tumor diameter and interstitial shadow. The interstitial shadow was clinically diagnosed as lymphangitis carcinomatosa and not ILD. Subsequently, the patient was treated with pembrolizumab, and the tumor showed much further shrinkage with no deterioration of the interstitial shadow. To date, the patient is alive with no complaints and no disease progression, and has continued pembrolizumab treatment for a total of 12 months. Lessons: In patients at a high risk of ICI-related side effects, platinum-doublet chemotherapy may be permitted as the first-line therapy for NSCLC with high PD-L1 expression. However, if the risk associated with ICIs is resolved, early switching from chemotherapy to pembrolizumab might be desirable, even if the chemotherapy is effective.