Complete Pathologic Response in Lung Tumors in Two Patients with Metastatic Non-small Cell Lung Cancer Treated with Erlotinib

Introduction: Patients with non-small cell lung cancer with a sensitizing mutation in the epidermal growth factor receptor ( EGFR) are likely to respond to treatment with an EGFR inhibitor. In some patients, residual tumor tissue can be visualized for several years without any signs of progression. Methods: Two patients with pathologically verified adenocarcinoma of the lung and multiple bone metastases were monitored after start of treatment with erlotinib by examining clinical parameters and imaging of lung tumors and bone metastases. Pretreatment biopsies and blood samples were examined for the presence of EGFR mutations, and lobectomy was performed according to standard procedures after 10 months of treatment in one patient and 30 months in the other. Results: Both patients responded to treatment with erlotinib and displayed a mutated EGFR. At the time of surgery, tumor was still visible in the lungs of both patients, but cancer cells could not be identified in the resected lung tumor tissue. In one patient, blood samples were available and the EGFR mutation was detected in the circulating DNA in the pretreatment blood sample but was no longer detectable 4 weeks after start of treatment and could not be detected in any of the following 12 blood samples. Conclusions: Treatment with erlotinib may induce complete response in patients with metastatic non-small cell lung cancer. It remains to be shown whether treatment with erlotinib can be discontinued in such patients. The disappearance of EGFR mutations in the DNA of the blood sample early in treatment might be used as an indicator of response to erlotinib.