Discordant EGFR mutation results: A case report

Background

Epidermal growth factor receptor (EGFR) is one of the driver mutations in advanced Non – Small Cell Lung Carcinoma (NSCLC) and is prominently chosen to advocate personalized treatment approaches. The advancing field of molecular pathology along with the introduction of the EGFR TKIs has profoundly changed the therapeutic landscape of the NSCLC. But therapeutic decision might be challenging when different testing methods yield non-identical results.

Method

A patient diagnosed with lung carcinoma negative for ALK and ROS1 rearrangements was subjected to EGFR testing by Therascreen, plasma based genotyping by Roche cobas V2 and bioRAD droplet digital PCR. Taking into consideration the variant results, both Therascreen and Roche cobas V2 testing was again performed on fresh biopsies.

Result

Single gene testing of EGFR by Therascreen was negative. Plasma based genotyping for EGFR mutations using the Roche cobas V2, yielding a del19 mutant whereas, bioRAD droplet digital PCR revealed del19 wild type along with small clone of T790M. The Therascreen assay was negative, whereas the Roche cobas V2 yielded a positive del19 mutant. The T790M clone was not detected by cobas neither in plasma nor in tissue.

Conclusion

In view of the absence of T790M mutant, the patient was planned first line therapy of Osimertinib. The choice of testing modality decides the suitable therapy for the patient to a great extent. Although tissue genotyping is still the gold standard, using liquid biopsy genotyping in addition to tissue genotyping improves the discovery of sensitizing mutations in targetable genes, ultimately leading to better patient outcomes.