Primary resistance to osimertinib despite acquired T790M

Serial Plasma Cell-Free Circulating Tumor DNA Tests Identify Genomic Alterations for Early Prediction of Osimertinib Treatment Outcome in EGFR T790M-Positive NSCLC

Introduction

Recent advances in the detection of genomic DNA from plasma samples allow us to follow tumor DNA shedding in plasma during systemic treatment. Osimertinib is the standard of care for patients with NSCLC with acquired EGFR T790M mutations. We assessed changes in serial plasma cell-free circulating tumor DNA (ctDNA) genomic alterations to predict osimertinib efficacy.

Methods

We prospectively collected plasma from patients having EGFR-mutated advanced NSCLC previously treated with EGFR tyrosine kinase inhibitor therapy and with acquired EGFR T790M mutation detected by standard methods. Plasma samples were collected before starting osimertinib treatment, 4 weeks after osimertinib treatment, and on progression. ctDNA was analyzed using the Guardant360 assay.

Results

A total of 15 eligible patients received osimertinib. Before starting treatment, EGFR-activating mutations were detected in the ctDNA of all patients, and EGFR T790M was detected in 93% of the cases. Osimertinib treatment was associated with an objective response rate of 53% and a median progression-free survival of 7.3 months. A total of 12 of the 15 patients had undetectable plasma T790M and decreased activating mutation allelic frequency (AF) at week 4. None of the 12 patients had disease progression within 16 weeks. For the remaining three patients, with detectable plasma T790M (n = 2) or increased activating mutation AF (n = 1) at week 4, two had progressive disease within 16 weeks (p = 0.03).

Conclusions

In patients with EGFR-mutated advanced NSCLC, persistent EGFR T790M or increasing activating mutation AF as detected in ctDNA 4 weeks after the start of osimertinib treatment may predict disease progression within 16 weeks.

Transformation of advanced lung adenocarcinoma to acquired T790M resistance mutation adenosquamous carcinoma following tyrosine kinase inhibitor: a case report

BACKGROUND

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) are recommended for patients with non-small cell lung cancer with EGFR mutations. However, acquired resistance to EGFR-TKIs seems inevitable and the mechanism of drug resistance has not been fully defined. There is no effective treatment for patients with advanced lung adenocarcinoma who are resistant to TKIs owing to pathologic type conversion.

CASE PRESENTATION

We report a patient who was initially diagnosed with lung adenocarcinoma. At first, she was sensitive to the first-generation TKI icotinib. After 17 months of treatment, the patient acquired resistance to icotinib. Moreover, after tumor resection, immunohistochemical analysis showed pathologic change from adenocarcinoma to adenosquamous carcinoma, and next-generation sequencing technology discovered EGFR exon19 p.745-750 del, exon20 p.T790M, and KMT2C exon 18 p.R973G mutations. After video-assisted tumor resection, the patient is receiving osimertinib (AZD 9291). Current overall survival is 60 months.

CONCLUSIONS

Surgical intervention may prolong survival time in patients with acquired TKI resistance, especially when there is no evidence of metastasis.

Secondary Resistant Mutations to Small Molecule Inhibitors in Cancer Cells

Secondary resistant mutations in cancer cells arise in response to certain small molecule inhibitors. These mutations inevitably cause recurrence and often progression to a more aggressive form. Resistant mutations may manifest in various forms. For example, some mutations decrease or abrogate the affinity of the drug for the protein. Others restore the function of the enzyme even in the presence of the inhibitor. In some cases, resistance is acquired through activation of a parallel pathway which bypasses the function of the drug targeted pathway. The Catalogue of Somatic Mutations in Cancer (COSMIC) produced a compendium of resistant mutations to small molecule inhibitors reported in the literature. Here, we build on these data and provide a comprehensive review of resistant mutations in cancers. We also discuss mechanistic parallels of resistance.