Stage IVB EGFR-mutated lung adenocarcinoma with brain metastases: complete response and pathologic complete response

What happened, in summary

A 60-year-old man with a smoking history was admitted in October 2023 after 1 month of cough and headache. CT showed a 4.2 x 3.2 cm mass in the left upper lung with hilar lymph-node enlargement, and brain MRI revealed multiple brain metastases. Lung biopsy confirmed pulmonary adenocarcinoma. Immunohistochemistry showed CK7, Napsin A, and TTF-1 positivity, with CK5/6, P40, and CD56 negativity. Genetic testing found an EGFR exon 21 mutation, c.2573 T>G p.Leu858Arg, at 10.5%, a MEK1 exon 3 mutation, c.335T>C p.Ile112Thr, at 40.3%, and high PD-L1 expression with TPS 95%. He was diagnosed with Stage IVB lung adenocarcinoma, cT2bN1M1c1. First-line treatment used pemetrexed 800 mg, lobaplatin 60 mg, and tislelizumab for 2 cycles. His cough and headache resolved, and CT after 2 months showed a partial response in the lung. He then received furmonertinib maintenance targeted therapy for 11 months. Side effects included diarrhea for 1 month and itching for 10 days, without grade 3 or higher adverse events. He did not need corticosteroids or anticonvulsants, and neurological function remained stable. In December 2024, imaging showed complete response of the brain metastases. After multidisciplinary review, he underwent thoracoscopic left upper lobectomy with lymph-node dissection. The operation found only minimal pleural adhesion and minor bleeding, with no air leak or acute respiratory distress afterward. Pathology showed ypT0N0M0, with no tumor in the lung specimen and 0 of 13 lymph nodes involved, confirming a pathologic complete response after systemic therapy.