Purpose: The purpose of the study is to evaluate the effect of gefitinib, an anti-EGFR TKI on circulating tumor cells (CTCs) in patients with metastatic breast cancer (MBC).
Methods: Seventeen patients with MBC with detectable CTCs after the completion of prior treatment received gefitinib 250 mg/day p.o. CTCs were monitored by immunofluorescence microscopy after double staining with anti-cytokeratin (A45-B/B3) and either anti-CD45 or anti-EGFR antibodies.
Results: A median reduction of 96.4 and 94.1 % in CTC count was observed in 11 (64.7 %) and 12 (70.6 %) of patients after the first and the second treatment cycles, respectively. Total CTC numbers declined by 73 and 44 % after the first and second treatment cycles, respectively. In nine patients with EGFR(+)/CK(+) CTCs, gefitinib resulted in a reduction of both EGFR(+) and EGFR(-) CTCs, and after the third course, most detected CTCs were EGFR(-). In two patients, with a sustained decrease in CTC numbers, a PFS of 16.0 and 19.0 months was observed and in one of them, it was associated with clinical objective response.
Conclusion: Treatment-resistant CTCs could be eliminated by gefitinib in MBC, and EGFR expression on CTCs merits further validation as a potential biomarker for specific and effective targeting of CTCs.
Trial registration: ClinicalTrials.gov NCT00428896.