Circulating tumor cells and FDG-PET/CT: biological and functional methods for therapeutic monitoring in metastatic breast cancer.

Abstract

#6052 Introduction: The combination of Computed Tomography (CT) and [18F] Fluorodeoxyglucose - Positron Emission Tomography (FDG-PET) scanning technologies provides a more complete picture of disease activity than CT alone. Circulating tumor cell (CTC) levels were shown to be more predictive than standard imaging (CT) when used to monitor disease progression in women with metastatic breast cancer (MBC). We performed a retrospective study to compare the ability of combined FDG-PET/CT to CTC to predict clinical outcomes in patients treated for MBC.
 Methods: One hundred and two MBC patients with either measurable or evaluable disease starting a new line of therapy had CTC counts and FDG-PET/CT scans done at baseline (BL) and at mid-therapy. CTC: 7.5mL of blood collected in CellSave tubes at both time points was assayed for CTC using the FDA approved CellSearch® System. Patients were categorized as having a favorable (<5CTC) or unfavorable (≥5CTC) outcome. Imaging: non-contrast-enhanced CT images were acquired first, then FDG-PET/CT scans were performed after administering a mean dose of 555 MBq FDG (range 444-740 MBq) to fasting patients. CT, PET, and co-registered CT-PET images were reviewed independently by 2 radiologists. The highest recorded FDG uptake was semi-quantitatively analyzed and maximum standardized uptake value (SUV) calculated with response = SUV of <50% in target lesions and no response = SUV of >50%. Changes in CTC and SUV at mid-therapy were compared to progression free survival (PFS) and overall survival (OS).
 Results: CTC: 50% (51/102) patients had ≥5 CTC at baseline (BL). At mid-therapy (median 2.5 months from BL), 21/102 progressed (≥5CTC) with a median PFS of 2.8 months vs. 7.8 months for those with no progression (<5CTC) (p<0.0001). OS was 10.0 months for patients with ≥5CTC at mid-therapy vs. 29.6 months for those with <5CTC (p<0.0001). PET/CT: 48% (49/102) patients showed no response at mid-therapy with median OS = 17.4 months vs. 29.6 months for those responding (p=0.0020). Overall, there was approximately 75% concordance in predicting outcomes between imaging and CTC assay changes [Table 1]. The majority of patients with discordant results had more advanced aggressive disease, i.e., >2nd line chemotherapy and triple-negative disease.
 
 Conclusion: ≥5 CTC and/or no response at FDG-PET/CT at mid-therapy accurately predicted significantly shorter OS. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6052.

Circulating tumor cell status monitors the treatment responses in breast cancer patients: a meta-analysis

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