Stage IV lung cancer: brain metastasis complete response after chemoimmunotherapy

What happened, in summary

A 66-year-old man with a 40-year smoking history was referred after a routine chest CT found a 5.2 x 4.8 cm solid nodule in the left upper lobe. He was asymptomatic, with well-controlled hypertension and no family history of cancer. PET-CT showed intense uptake in the lung nodule, and no other abnormal uptake was seen at that time. Chest CT showed no mediastinal lymphadenopathy or pleural effusion. Pathology revealed mixed poorly differentiated non-small cell lung cancer with neuroendocrine features, including solid growth, focal glandular differentiation, frequent mitoses, and necrosis. Immunohistochemistry showed partial loss of BRG-1 expression, with about 40% of tumor cells retaining nuclear staining. Molecular testing found a KRAS mutation, and PD-L1 testing showed TPS 5% and CPS 20. The initial clinical stage was Stage IIB, so the team chose surgical resection because the disease appeared early-stage and he had good performance status. After surgery, he received adjuvant etoposide plus cisplatin because of the poorly differentiated histology and neuroendocrine features. A postoperative brain MRI then detected a 0.6 x 0.5 cm enhancing lesion in the right cerebellar hemisphere, consistent with metastasis, moving the disease into a metastatic course. Treatment shifted to carrelizumab, a PD-1 inhibitor, combined with paclitaxel and carboplatin. He initially tolerated therapy with only grade 1 fatigue and nausea. Follow-up chest CT showed postsurgical changes only, and brain MRI showed complete resolution of the cerebellar metastasis. Later, he developed immune-mediated adrenocortical insufficiency with muscle weakness and decreased appetite, which resolved after systemic glucocorticoid treatment.