Stage 4 small cell lung cancer with paraneoplastic neurological syndrome

What happened, in summary

A 69-year-old woman with a 47-pack-year smoking history was evaluated for more than 1 month of fatigue, anorexia, and cough. Blood tests showed hyponatremia, with sodium of 122 mEq/L, and markedly elevated pro-GRP at 3666 pg/mL. PET/CT, brain MRI, and bronchoscopy led to a diagnosis of extensive-stage small cell lung cancer in the left upper lobe, staged cT4N3M1b with lymph-node metastasis, including left axillary nodes. Because her performance status was 3, treatment began with carboplatin and etoposide without immunotherapy. After 2 courses, the lung cancer and nodal metastases rapidly shrank, her fatigue and anorexia improved, and her performance status improved to 1. Atezolizumab was then added for the third course, and after 4 total courses, she began maintenance atezolizumab 1200 mg every 3 weeks. Around the second chemotherapy course, she developed numbness in the hands and feet, constipation, and walking instability. These symptoms worsened during atezolizumab maintenance, with orthostatic hypotension and declining function, so atezolizumab was discontinued. Testing showed multiple paraneoplastic antibodies, including anti-Hu, anti-AMPH, anti-Ri, anti-SOX-1, and anti-Zic4. She also developed atezolizumab-related destructive thyroiditis and received levothyroxine. Neurological treatment included duloxetine, mecobalamin, pregabalin, intravenous methylprednisolone, prednisolone, and IVIG. Her sensory symptoms persisted, but walking instability, orthostatic hypotension, and constipation improved. Over the next 2 years, CT scans showed stable complete response of the lung cancer, normal tumor markers, no new metastases, and no neurological worsening. The durable cancer response allowed clinicians to focus on symptom control and immune/paraneoplastic complications rather than restarting atezolizumab maintenance in a patient whose neurologic function remained vulnerable.