Metastatic lung adenocarcinoma with brain and iliac bone response to chemoimmunotherapy

What happened, in summary

A 68-year-old man was found to have a right lower-lobe lung nodule in August 2020 and underwent surgical resection. Pathology showed Stage IA right lower-lobe lung adenocarcinoma, pT1N0M0, and no adjuvant therapy was given. Molecular testing found no detectable EGFR, ALK, ROS1, RET, KRAS, BRAF, MET, HER2, or NTRK alteration, and PD-L1 expression was negative. More extensive testing for TMB, MSI-H, and mismatch-repair deficiency was not performed. In February 2022, the cancer returned with a painful left iliac bone metastasis and multiple brain metastases, without new lesions elsewhere. Radiation was directed only to the left iliac bone, using IMRT at 36 Gy in 12 fractions for pain relief. During that radiation course, he received pemetrexed disodium, cisplatin, and sintilimab. Follow-up brain MRI 1 month later showed complete remission of the brain metastases even though he had not received cranial radiation. He then received 2 additional cycles of pemetrexed, cisplatin, and sintilimab, but developed grade 3 rash and gastrointestinal toxicity. Treatment was changed to carboplatin, pemetrexed, and sintilimab for 2 cycles, followed by maintenance sintilimab for 24 months, with or without alternating pemetrexed. Later tissue testing identified a TP53 mutation with VAF 4.8%. During surveillance, CEA and CYFRA 21-1 progressively declined and stabilized at low levels, while CD8-positive T-cell counts stayed elevated. Follow-up frequency was later reduced to quarterly assessment after the 2-year treatment course. At last follow-up, lung, bone, and brain lesions remained stable, progression-free survival was 35 months, and overall survival exceeded 40 months. The durable response included both irradiated bone disease and non-irradiated brain disease.