An observational study of circulating tumor cells and (18)F-FDG PET uptake in patients with treatment-naive non-small cell lung cancer

Abstract

Introduction: We investigated the relationship of circulating tumor cells (CTCs) in non-small cell lung cancer (NSCLC) with tumor glucose metabolism as defined by (18)F-fluorodeoxyglucose (FDG) uptake since both have been associated with patient prognosis.

Materials & methods: We performed a retrospective screen of patients at four medical centers who underwent FDG PET-CT imaging and phlebotomy prior to a therapeutic intervention for NSCLC. We used an Epithelial Cell Adhesion Molecule (EpCAM) independent fluid biopsy based on cell morphology for CTC detection and enumeration (defined here as High Definition CTCs or "HD-CTCs"). We then correlated HD-CTCs with quantitative FDG uptake image data calibrated across centers in a cross-sectional analysis.

Results: We assessed seventy-one NSCLC patients whose median tumor size was 2.8 cm (interquartile range, IQR, 2.0-3.6) and median maximum standardized uptake value (SUVmax) was 7.2 (IQR 3.7-15.5). More than 2 HD-CTCs were detected in 63% of patients, whether across all stages (45 of 71) or in stage I disease (27 of 43). HD-CTCs were weakly correlated with partial volume corrected tumor SUVmax (r = 0.27, p-value = 0.03) and not correlated with tumor diameter (r = 0.07; p-value = 0.60). For a given partial volume corrected SUVmax or tumor diameter there was a wide range of detected HD-CTCs in circulation for both early and late stage disease.

Conclusions: CTCs are detected frequently in early-stage NSCLC using a non-EpCAM mediated approach with a wide range noted for a given level of FDG uptake or tumor size. Integrating potentially complementary biomarkers like these with traditional patient data may eventually enhance our understanding of clinical, in vivo tumor biology in the early stages of this deadly disease.

Figure 1. Detecting Putative DAPI(+), CK(+), CD45(-) HD-CTCs by Fluid Biopsy.

A representative image of High Definition Circulating Tumor Cells (HD-CTCs) from a Stanford patient with stage I non-small cell lung cancer shown in composite immunofluorescence (A) and by Wright-Giemsa brightfield microscopy (B). HD-CTCs are characterized as 4′,6-diamidino-2-phenylindole (DAPI) positive with a nucleus that is larger than surrounding white blood cells (Blue, C), cytokeratin (CK) positive (Red, D) and CD45 leukocyte marker negative (Green, E).

Figure 2. Non-small Cell Lung Cancer FDG PET-CT Imaging Features.

A three dimensional, maximum intensity projection, whole body ¹⁸F-FDG PET-CT (left). Physiologic uptake is seen in the brain, heart and liver with excretion through the renal pelvis and bladder. This tumor showed an intense FDG uptake with SUV_max of 19, SUV_mean of 9.6, and TLG of 65.6 using a 50% SUV_max threshold (upper right). On CT, the lesion volume was estimated at 6.0 cm³ with a maximum diameter of 22 mm (lower right).

Figure 3. FDG Uptake and CTC Features Correlation Matrix*.

TLG = Total Lesion Glycolysis; SUV = Standardized Uptake Value; PVC = Partial Volume Corrected; 10 M WBC = 10 Million White Blood Cells. Bolded numbers are significant by p-value <0.05. Half of the matrix only is presented since it is symmetric around one and correlations are shaded by the magnitude of correlation. *Spearman rank correlations are shown for 62 of 71 patients with data extracted by PET-VCAR.

Figure 4. HD-CTC Scatter Plots for SUV_maxPVC and CT diameter*.

Non-metastatic patients are highlighted in red (see methods for definition) and the axes are shown as log₂(x,y) for ease of interpretation. Increasing SUV_maxPVC (left) was weakly correlated (r = 0.27, p-value = 0.03) with increasing HD-CTC/10 M WBC count compared to tumor diameter on CT (right; r = 0.07, p-value = 0.60), which showed no correlation. *Shown for 62 of 71 patients with data extracted by PET-VCAR.