Long-Term Responders to Erlotinib for Pulmonary Adenocarcinoma With Wild-Type Epidermal Growth Factor Receptor: Two Case Reports and a Single-Institutional Retrospective Study

Erlotinib is an oral and reversible epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor and is now used exclusively to non-small cell lung carcinoma (NSCLC) harboring mutated EGFR. However, there was historically a transient period when erlotinib was widely used regardless of EGFR mutation status. We report two cases with adenocarcinoma and wild-type EGFR status, which responded to erlotinib for unusual long time. We also retrospectively analyzed patients with adenocarcinoma and wild-type EGFR mutation status who had received erlotinib-containing regimen in our hospital. A 60-year-old woman received the second-line and tri-weekly regimen of pemetrexed (500 mg/m(2) on day 1) and intermittent erlotinib (150 mg on days 2 - 16). Pemetexed was discontinued 18 months after the initiation of this regimen, but erlotinib was continued for more than 11 years. This chemotherapy successfully reduced her brain metastasis and prevented recurrence. A 58-year-old man received erlotinib monotherapy as the third-line regimen, by which multiple brain metastases disappeared. Although we tried stopping erlotinib 9 years after the initiation of erlotinib, a solitary metastasis appeared in the brain 3 months after the discontinuation of erlotinib. Between December 2007 and October 2015, 39 patients with wild-type EGFR status initiated erlotinib-containing regimens at our hospital. The response rate, progression-free survival and overall survival were 17.9% (95% confidence interval (CI): 7.5-33.5%), 2.7 months (95% CI: 1.8 - 5.0 months) and 10.3 months (95% CI: 5.0 - 15.7 months), respectively. We reported two long-term responders and survivors to erlotinib for more than 9 years, which was much longer than patients with adenocarcinoma and wild-type EGFR mutation status who had received erlotinib-containing regimen in our hospital.