What happened, in summary

A 79-year-old woman underwent lobectomy in 2015 for lung adenocarcinoma classified pT1a pN1 M0 and received no adjuvant treatment. Mediastinal lymph nodes appeared the following year, and biopsy confirmed recurrence with PD-L1 expression of 100%. Pembrolizumab 200 mg every three weeks was started.

Within one week, she developed an itchy grade 2 rash affecting about 20% of her body. Antihistamine and topical corticosteroids controlled but did not fully eliminate it. After the third infusion, chest pain led to detection of an 8 mm pericardial effusion. Methylprednisolone resolved the symptoms and effusion, allowing pembrolizumab to restart under close cardiac monitoring.

After the sixth infusion, she developed severe diarrhoea and CT evidence of colitis. Intravenous methylprednisolone stopped the diarrhoea within 24 hours. Because imaging showed a complete cancer response, pembrolizumab was permanently discontinued. Three months later, profound weakness, ptosis, and dysarthria led to a diagnosis of seronegative myasthenia gravis. Pyridostigmine and corticosteroids were insufficient, but five plasmapheresis treatments produced rapid improvement.

Six months after pembrolizumab ended, CT scans still showed complete oncologic response. The major immune complications had resolved, she was physically well without corticosteroids, and pyridostigmine was being tapered, although mild pruritus persisted.