Sensitizing mutations
The more commonly used strategy for blocking EGFR signaling in lung cancer is the use of tyrosine kinase inhibitors, which compete with adenosine triphosphate (ATP) for binding to the tyrosine kinase portion of the receptor. They are located at chromosome 7p11.2. The most frequent mutations that sensitize patients to EGFR inhibitors include exon 19 deletions and L858R point mutation in exon 21, although multiple other driver mutations also exist.
The first-generation of EGFR TKIs include gefitinib and erlotinib, which bind reversibly to the EGF receptor. Second-generation inhibitors afatinib and dacomitinib bind irreversibly. Osimertinib, a third-generation EGFR TKI, which also binds irreversibly, was approved in 2020 for adjuvant therapy, and first- and second-line treatment in patients with NSCLC who have EGFR mutation–positive disease.
First-generation EGFR tyrosine kinase inhibitors
Four randomized, first-line, placebo-controlled phase 3 trials conducted with EGFR TKIs in combination with platinum-based doublet chemotherapy in an EGFR nonselected patient population failed to show a survival benefit with erlotinib or gefitinib (TRIBUTE, Tarceva Lung Cancer Investigation Trial, INTACT 1, INTACT 2).
However, a first-line study randomized patients to gefitinib or chemotherapy with carboplatin-paclitaxel, and included patients with or without an EGFR mutations. In the subgroup of patients with an EGFR mutation, progression-free survival (PFS) was significantly longer among those who received gefitinib than among those who received carboplatin–paclitaxel (hazard ratio for progression or death, 0.48), whereas in the subgroup of patients who were negative for the mutation, PFS was significantly longer among those who received chemotherapy (HR for progression or death with gefitinib, 2.85).
Numerous studies have shown that EGFR TKIs used in the first-line setting improved progression free survival, response rates, and quality of life while reducing toxicity. A recent meta-analysis of randomized clinical trials involving EGFR TKIs showed that EGFR TKI improved PFS with a HR of 0.40, compared with standard chemotherapy with fewer serious adverse events, although no benefit on overall survival was observed (HR, 0.96; 95% confidence interval, 0.83-1.10; P = .556).
T790M: The most common resistance mutation
T790M is the most common resistance mechanism to develop in patients with EGFR mutations being treated with EGFR TKIs. A randomized phase 3 trial of osimertinib vs. chemotherapy in patients with T790M-positive advanced NSCLC who had disease progression after first-line EGFR-TKI therapy, reported a median duration of progression-free survival that was significantly longer with osimertinib than with platinum therapy plus pemetrexed (10.1 months vs. 4.4 months; HR, 0.30). In addition, among 144 patients with metastases to the central nervous system, the median duration of PFS was longer among patients receiving osimertinib than among those receiving platinum therapy plus pemetrexed (8.5 months vs. 4.2 months; HR, 0.32). However, now that osimertinib has moved into the front-line setting, it has left a void for the treatment of patients with advanced disease who have failed osimertinib.