Rare EGFR Mutation Shows Primary Resistance to Afatinib in Lung Cancer Case

A 68-year-old man with stage IV lung adenocarcinoma carrying an uncommon EGFR mutation called p.E709_T710delinsD experienced rapid disease progression despite treatment with the targeted drug afatinib, according to a case report published in Frontiers in Oncology by physicians at The First People's Hospital of Changde City in China. The patient, who also had brain metastases at the time of diagnosis, died five weeks after starting therapy, an outcome the authors describe as a rare example of primary resistance to afatinib in this molecular subset of non-small cell lung cancer (NSCLC). The EGFR p.E709_T710delinsD variant is an in-frame deletion-insertion mutation located in exon 18 of the EGFR gene.

It belongs to a structural class known as P-loop and alpha-C-helix compressing (PACC) mutations, in which the genetic change compresses the kinase domain's key regulatory elements. That expectation makes the observed treatment failure clinically notable rather than merely anecdotal. Molecular testing at baseline revealed a variant allele frequency of 45.9 percent for the p.E709_T710delinsD mutation, indicating that nearly half of the tumor cells carried the alteration.

The testing also detected co-occurring EGFR amplification, with a fold change of 1.5, meaning extra copies of the EGFR gene were present alongside the mutation. Both features were documented in a patient whose disease had already spread to the brain when treatment began, a combination of high mutation abundance, additional EGFR driver events, and extensive baseline disease burden. The patient received oral afatinib at an initial dose of 30 milligrams once daily.

Rather than shrinking or stabilizing, the disease progressed rapidly, a pattern the authors interpret as possible primary targeted resistance, meaning the tumor showed no initial benefit from the drug at all. The authors are careful about what the case can and cannot establish. No tissue sample or additional molecular evidence was available to confirm the specific mechanism behind the treatment failure, so the report combines the single observation with a review of previous literature to explore potential contributing factors and their clinical implications.

Importantly, they state that the case does not refute the overall sensitivity of the p.E709_T710delinsD variant to afatinib. Instead, it suggests that in patients presenting with high baseline disease burden and aggressive tumor biology, this variant may occasionally manifest as a phenotype in which initial benefit is absent and progression is swift. Brain metastases add a further layer of complexity to cases like this one.

From a technical standpoint, the case raises questions about how co-occurring genomic alterations shape response to targeted therapy. Without repeat biopsy or plasma-based analysis, however, none of these possibilities could be confirmed in this patient. Based on this experience and the assembled literature, the authors offer a practical recommendation for clinicians encountering similar presentations.

The report ultimately serves as a reminder that even well-characterized predictive mutations do not guarantee response in every patient. Single case reports cannot establish how frequently primary resistance occurs in the p.E709_T710delinsD population, and the authors explicitly frame their contribution as hypothesis-generating rather than definitive. But for oncologists treating NSCLC patients with rare EGFR variants, the message is concrete: monitor closely from the first weeks of therapy, and when the disease moves against expectations, move quickly to find out why.

Subject of Research: Primary resistance to afatinib in NSCLC harboring the rare EGFR p.E709_T710delinsD PACC mutation

Article Title: Primary resistance to afatinib in a patient with NSCLC harboring EGFR p.E709_T710delinsD and brain metastases: a case report and literature review

Article References: Dong, S.-S., Zhang, X., & Dong, W. (2026). Primary resistance to afatinib in a patient with NSCLC harboring EGFR p.E709_T710delinsD and brain metastases: a case report and literature review. Frontiers in Oncology, 16, Article 1981577. https://doi.org/10.3389/fonc.2026.1981577

Image Credits: AI Generated

DOI: 10.3389/fonc.2026.1981577

Keywords: EGFR p.E709_T710delinsD, afatinib, primary resistance, non-small cell lung cancer, PACC mutation, brain metastases, EGFR amplification, ctDNA, lung adenocarcinoma, targeted therapy, case report, Primary