Inflamed Tumor Phenotype as Predictor of Long-Term Response to Pembrolizumab in an EGFR-Mutated Non-Small Cell Lung Cancer (NSCLC) Patient with Acquired Resistance to Afatinib: a Case Report and Review of the Literature

Treatment with immune checkpoint inhibitors (ICIs) that target the programmed cell death 1/programmed cell death ligand-1 (PD-1/PD-L1) axis is usually ineffective in patients with epidermal growth factor receptor (EGFR)-mutated advanced non-small cell lung cancer (NSCLC), either as first-line treatment or in later lines. By contrast, especially for patients with common EGFR mutations (exon 19 deletion/L858R point mutation), an orally bioavailable EGFR tyrosine kinase inhibitor (EGFR-TKI) is the best upfront therapy, being able to provide response rates well above 50% and a median progression-free survival ranging from 11 to 19 months, depending on whether a second-generation (e.g., afatinib) or a third-generation (i.e., osimertinib) EGFR-TKI is used. Unfortunately, treatment options for these patients at the time of acquired resistance are limited. As for afatinib-pretreated patients, those who develop a T790M mutation may benefit from osimertinib, whereas platinum-based chemotherapy is the preferable therapeutic strategy for T790M-negative patients as well as for patients who progress on osimertinib administered as first-line therapy. Here, we describe the case of an exon-19-deleted patient who experienced a complete response to the anti-PD-1 agent pembrolizumab upon the development of T790M-negative acquired resistance to afatinib. Furthermore, we discuss this case in the context of the existing literature, especially focusing on the importance of evaluating multiple markers of immune response post-EGFR-TKI and prior to ICI treatment in order to select the best treatment strategy in this clinical scenario.