What happened, in summary

A 64-year-old woman with a 40 pack-year smoking history was found to have a large right upper-lobe lung mass during preoperative testing for a separate breast cancer. CT showed a 6.1 × 5.2 cm right lung mass and a 2 × 1.8 cm left upper-lobe nodule. Biopsy of the left lesion showed poorly differentiated non-small cell carcinoma favouring pulmonary adenocarcinoma, with PD-L1 expression of 70%. PET/CT demonstrated extensive mediastinal and hilar nodal disease, both lung lesions, and a hypermetabolic lytic focus in the left iliac bone. Brain MRI was negative. The lung cancer was classified as stage IVA, cT4 cN3c M1b. She declined chemotherapy because of its likely effect on quality of life and began pembrolizumab as palliative immunotherapy. After three cycles, PET/CT showed a mixed response with mild overall improvement. Her white blood cell count then rose dramatically above 140 × 10⁹/L despite treatment of an E. coli urinary infection and repeated bone-marrow studies showing no leukaemia. She developed painful leg ulcers and limb-threatening arterial insufficiency, requiring anticoagulation, right femoral endarterectomy, and leukapheresis. Clinicians considered the extreme leukocytosis a paraneoplastic leukemoid reaction contributing to hyperviscosity and arterial thrombosis. She subsequently developed acute hypoxic respiratory failure. In keeping with her wishes, care became comfort focused, and she died the following day.