Long-Term Cutaneous Hyperpigmentation During Adjuvant Osimertinib Therapy in a Resected Stage IIB EGFR L858R-Mutated Lung Adenocarcinoma in an Older Adult: A Rare Case Report with Two-Year Follow-Up and Literature Review.

The use of targeted therapies has improved outcomes in patients with resected epidermal growth factor receptor-mutated non-small cell lung cancer, but uncommon and persistent dermatologic toxicities remain poorly characterized. We report a 71-year-old woman with resected lung adenocarcinoma harboring an epidermal growth factor receptor exon 21 L858R mutation. Following right upper lobectomy and systematic mediastinal lymph node dissection, pathological staging was pT2aN1M0 (stage IIB). She received four cycles of adjuvant cisplatin plus pemetrexed followed by planned three-year adjuvant Osimertinib. During Osimertinib treatment, she developed a persistent violaceous rash accompanied by progressive cutaneous hyperpigmentation. Osimertinib was temporarily interrupted, and dermatologic evaluation was performed, resulting in partial clinical improvement. Hyperpigmentation, however, persisted during follow-up. Other adverse events included grade 1 diarrhea, transient arthralgia, anorexia, and weight loss. Osimertinib was subsequently resumed and maintained. Nearly two years after surgery, the patient remains free of disease recurrence, with stable pigmentary skin changes. This case highlights an uncommon and prolonged dermatologic manifestation associated with Osimertinib and emphasizes the importance of recognizing atypical cutaneous toxicity to facilitate appropriate management and to facilitate appropriate dermatologic evaluation and individualized management of treatment-related toxicity.