Poster Session : PS 1433 ; Hemato-Oncology(Oncology) : Systemic Nocardiosis Mimicking Disease Flare-Up After Discontinuation of Gefitinib in a Patient with EGFR-Mutant Lung Cancer

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKI) tend to be dramatically effective in patients with non-small cell lung cancer (NSCLC) harboring sensitizing EGFR mutations. However, most of the patients with EGFR-mutant lung cancer who have initially shown response to EGFR-TKI eventually acquire resistance to the drug. Moreover, a few of them experience accelerated progression of disease on discontinuation of EGFR-TKI. Thus, even after radiologic progression, maintenance of EGFR-TKI until administration of another effective treatment is recommended in this patient group. A 56-year-old man with recurrent EGFR-mutant lung cancer metastatic to the brain was treated with fifteen cycles of gefitinib, until when progression in the lung was demonstrated on restaging CT scan. While he was on the eleventh cycle of gefitinib, the patient underwent stereotactic radiosurgery (SRS) for his brain lesion causing right hemiparesis, but grew dependent on corticosteroid afterwards due to development of cerebral necrosis with recurrent right-sided weakness. As his lung lesions more than doubled over two weeks after discontinuation of the EGFR-TKI, however, gefitinib was resumed under the impression of fiare-up of the gefitinib-sensitive lung cancer. Three weeks later, the EGFR-TKI retrial proved ineffective, both from clinical findings and from multiple new lesions in the lung and brain on restaging imaging. Subsequent brain biopsy revealed abscess material, and a sputum culture grew Nocardia species, making a final diagnosis of systemic nocardiosis, rather than cancer fiareup. Both fiare-up of EGFR-mutant lung cancer and disseminated infection of any sorts can lead to rapid clinical deterioration, but can overlap in their clinical presentation. High index of suspicion, therefore, is required to differentiate between them, and confirmative evaluation such as percutaneous biopsy might be of help to guide further therapeutic management in appropriate clinical setting.