Purpose: Circulating tumor cells (CTCs) can be detected in the bloodstream of cancer patients in diverse epithelial cancers and elevated levels or increases in CTC counts portend poor prognosis. Less is known about the potential application of CTCs as surrogate endpoints, or as a source of cells for predictive biomarker evaluation in patients with advanced cancer enrolled in early phase clinical trials. This study investigated the feasibility of CTC enumeration, phenotypic characterization, as well as oncogenic mutation detection from CTCs and circulating tumor DNA (ctDNA) in patients with advanced lung cancer enrolled in a global multi-center, phase II clinical trial.

Patients and Methods: Forty-one patients with advanced NSCLC who had received at least one prior chemotherapy regimen were enrolled in a phase 2, single-arm clinical study of the combination therapy with erlotinib and pertuzumab. Erlotinib is a small molecule inhibitor of epidermal growth factor receptor (EGFR), and pertuzumab is a monoclonal antibody that blocks HER2 dimerization with other HER family receptors. Peripheral blood was collected prior to the start of therapy and during the course of the study. Analyses in CTCs included enumeration, evaluation of EGFR expression and detection of oncogenic mutations in both CTCs and ctDNA and correlations were made to tumor response as measured by tumor FDG-PET changes or by computed tomography (CT) imaging.

Results: CTC were detected (≥1 CTC) at baseline in 78% of patients (n=30). EGFR expression was evaluated in CTCs by immunofluorescence and revealed a range of expression levels and substantial heterogeneity for this biomarker in CTCs. Greater sensitivity for mutation detection was observed in ctDNA when compared to CTCs across a 6-gene panel (EGFR, KRAS, BRAF, NRAS, AKT1 and PIK3CA). Importantly, mutation detection in ctDNA was highly concordant with mutation status in patient tumor. Higher baseline CTC counts were observed in patients with EGFR mutations or with other oncogenic activating mutations, suggesting that CTC counts may be associated with underlying tumor genotype. A trend toward lower CTC counts was observed across on-treatment time-points, with statistically significant decreases in CTC counts (p=0.02) observed in either FDG-PET or RECIST responders. In comparison, no significant decreases were observed in non-responders.

Conclusion: We demonstrate feasibility of enumeration and phenotypic characterization in CTCs and mutation detection in ctDNA from NSCLC patients in a global, multi-center Phase II study. In addition, our data provides the first evidence of a possible correlation between decreases in CTC counts and response by either FDG-PET or RECIST in patients with advanced NSCLC. These findings will require prospective validation but suggest a potential future role for using CTC decreases as an early indication of response to therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr PR-3.