What happened, in summary

This 75-year-old woman had a prior history of poorly differentiated, high-grade squamous cell carcinoma of the right upper lobe, treated 10 years earlier with lobectomy and adjuvant gemcitabine-cisplatin. During annual CT surveillance, a new 33 × 29 × 22 mm lesion appeared in the left upper lobe. PET showed a hypermetabolic lesion with pleural extension, and endoscopic ultrasound-guided biopsy confirmed adenocarcinoma with lepidic and micropapillary components. Mediastinal nodes sampled at stations 4L, 7, 11L, and 11R were not involved. She underwent left upper-lobe segmentectomy with systematic mediastinal lymph-node sampling. Pathology showed invasive micropapillary adenocarcinoma, grade 3, with spread through air spaces and a 0.4 cm surgical margin. The tumor was considered a second metachronous primary lung cancer and was staged pT2aN0M0. PD-L1 expression was less than 1%, and next-generation sequencing found no actionable alterations in EGFR, ALK, KRAS, BRAF, MET, PIK3CA, RET, ROS1, or NTRK1-3. Because of high-risk histologic features, she received adjuvant pembrolizumab 200 mg every 21 days through an off-label compassionate-use protocol. Pembrolizumab was stopped after 17 cycles because of persistent ALT, AST, and ALP elevation. Corticosteroids were not needed, liver enzymes normalized by 5 months, and PET-CT at 6-month oncologic follow-up showed complete metabolic response with no residual disease. Viral hepatitis and other causes of drug-induced liver injury were excluded, and her bilirubin, albumin, and coagulation tests stayed within normal ranges. That allowed the liver toxicity to be managed by stopping pembrolizumab rather than adding corticosteroids. The cancer assessment remained favorable, with no mediastinal nodal involvement at diagnosis and no residual metabolic disease at follow-up.