[Hyponatremia in a 58-year-old female patient with EGFR-positive lung adenocarcinoma].

The case of a 58-year old female patient with epidermal growth factor-positive pulmonary adenocarcinoma treated with the tyrosine kinase inhibitor afatinib is reported. After several months of first-line therapy the patient developed severe hyponatremia and tumor reassessment revealed a progressive course of the lung cancer. Rebiopsy showed transformation of the tumor into small-cell lung cancer. Therapy with afatinib was stopped immediately and platin-based chemotherapy was started. This case shows that tumor transformation under tyrosine kinase inhibitor therapy from non-small-cell into small-cell lung cancer can occur in rare cases.