Exhaled breath condensate confirming T790M mutation in EGFR-mutated Non-Small Cell Lung Cancer

We report a case of metastatic Non-Small Cell Lung Cancer (NSCLC) with Epidermal Growth Factor Receptor (EGFR) sensitizing mutation - deletion exon 19 - treated with first line chemotherapy using Carboplatin and Pemetrexed. The treatment was then changed to first generation tyrosine kinase inhibitor (TKI), Gefinitib following the detection of EGFR sensitizing mutation. Upon disease progression on Gefitinib, the need for tissue biopsy for resistant point mutation that substitutes methionine for threonine at amino acid position 790 (T790M) was met with diagnostic challenge due to difficulty in sampling tissue from the site of progressive disease. We opted, instead, to perform the non-invasive method using exhaled breath condensate (EBC) and plasma circulating tumour DNA (ctDNA); both of these tests detected the presence of T790M mutation. Third generation TKI, Osimertinib, was commenced based on these non-invasive diagnostic methods, and the patient showed partial response followed by ongoing stable disease after 28 months which exceeded the median progression-free survival (PFS) demonstrated in the AURA3 trial. We believe that a non-invasive method using novel EBC or plasma ctDNA can be used not only as an adjunct test but as an alternative to tissue biopsy where there are diagnostic challenges with invasive procedures.