# Advanced lung adenocarcinoma harboring uncommon EGFR 19 Del and T790M/trans-C797S mutations after resistance: a case report and literature review

## TL;DR

A lung cancer patient with rare EGFR mutations responded well to a combination of first- and third-generation drugs, offering a new treatment approach.

## Contribution

Reports a rare case of EGFR 19Del with T790M and trans-C797S mutations and a successful treatment strategy.

## Key findings

- Patient with uncommon EGFR mutations showed positive response to combined TKI therapy.
- Combination of first- and third-generation TKIs may be effective against trans-C797S resistance mutations.
- Case highlights the potential for tailored treatment in patients with complex EGFR mutations.

## Abstract

The most common epidermal growth factor receptor (EGFR) mutation in non-small cell lung cancer (NSCLC) is exon 19 deletion (19del), which is sensitive to EGFR tyrosine kinase inhibitors (EGFR-TKIs). However, uncommon EGFR 19del mutations exhibit varied responses to EGFR-TKI treatment. Research and clinical data on these uncommon subtypes are limited. Additionally, resistance to EGFR-TKIs is inevitable. EGFR C797S is a frequent mechanism of resistance to third-generation EGFR-TKIs, usually occurs in cis with T790M and in 5% of patients in trans. Here, we report a patient diagnosed with lung adenocarcinoma harboring EGFR 19Del L747-A755delinsSKD mutation with co-occurring T790M and trans-C797S mutations, who showed a positive response to combination therapy with first- and third-generation TKIs. This case report suggests an effective treatment option for such patients.