Prospective evaluation of whole-body MRI and 18F-FDG PET/MRI in N and M staging of primary breast cancer patients

Abstract

Objectives: To evaluate and compare the diagnostic potential of whole-body MRI and whole-body ¹⁸F-FDG PET/MRI for N and M staging in newly diagnosed, histopathologically proven breast cancer.

Material and methods: A total of 104 patients (age 53.4 ± 12.5) with newly diagnosed, histopathologically proven breast cancer were enrolled in this study prospectively. All patients underwent a whole-body ¹⁸F-FDG PET/MRI. MRI and ¹⁸F-FDG PET/MRI datasets were evaluated separately regarding lesion count, lesion localization, and lesion characterization (malignant/benign) as well as the diagnostic confidence (5-point ordinal scale, 1-5). The N and M stages were assessed according to the eighth edition of the American Joint Committee on Cancer staging manual in MRI datasets alone and in ¹⁸F-FDG PET/MRI datasets, respectively. In the majority of lesions histopathology served as the reference standard. The remaining lesions were followed-up by imaging and clinical examination. Separately for nodal-positive and nodal-negative women, a McNemar chi² test was performed to compare sensitivity and specificity of the N and M stages between ¹⁸F-FDG PET/MRI and MRI. Differences in diagnostic confidence scores were assessed by Wilcoxon signed rank test.

Results: MRI determined the N stage correctly in 78 of 104 (75%) patients with a sensitivity of 62.3% (95% CI: 0.48-0.75), a specificity of 88.2% (95% CI: 0.76-0.96), a PPV (positive predictive value) of 84.6% % (95% CI: 69.5-0.94), and a NPV (negative predictive value) of 69.2% (95% CI: 0.57-0.8). Corresponding results for ¹⁸F-FDG PET/MRI were 87/104 (83.7%), 75.5% (95% CI: 0.62-0.86), 92.2% (0.81-0.98), 90% (0.78-0.97), and 78.3% (0.66-0.88), showing a significantly better sensitivity of ¹⁸F-FDG PET/MRI determining malignant lymph nodes (p = 0.008). The M stage was identified correctly in MRI and ¹⁸F-FDG PET/MRI in 100 of 104 patients (96.2%). Both modalities correctly staged all 7 patients with distant metastases, leading to false-positive findings in 4 patients in each modality (3.8%). In a lesion-based analysis, ¹⁸F-FDG PET/MRI showed a significantly better performance in correctly determining malignant lesions (85.8% vs. 67.1%, difference 18.7% (95% CI: 0.13-0.26), p < 0.0001) and offered a superior diagnostic confidence compared with MRI alone (4.1 ± 0.7 vs. 3.4 ± 0.7, p < 0.0001).

Conclusion: ¹⁸F-FDG PET/MRI has a better diagnostic accuracy for N staging in primary breast cancer patients and provides a significantly higher diagnostic confidence in lesion characterization than MRI alone. But both modalities bear the risk to overestimate the M stage.

Keywords: Breast cancer staging; MRI; PET/MRI.

Fig. 1

Determination of the lymph node stage with MRI alone (a) and ¹⁸F-FDG PET/MRI (b)

Fig. 2

A 57-year old woman with diagnosis of primary breast cancer. Primary tumor located in the left breast and visible bone metastasis in a left rib with contrast enhancement on T1w fs VIBE (a), corresponding diffusion restriction (c), and pathological FDG uptake on PET (d) and fused ¹⁸F-FDG PET/MRI (b)

Fig. 3

A 47-year old woman with primary breast cancer on the left side. Visible enlarged axillary lymph node with contrast enhancement in T1w fs VIBE (a) and corresponding diffusion restriction (c) as well as a pathological FDG uptake on PET (d) and fused ¹⁸F-FDG PET/MRI (b), rated as an axillary lymph node metastasis

Fig. 4

A 61-year old woman with diagnosis of primary breast cancer. Not enlarged, ovoid axillary lymph nodes in T1w fs VIBE without contrast enhancement and with visible fatty hilum (a). No evidence of a clear diffusion restriction (c). However, a pathological FDG uptake on PET (d) and fused ¹⁸F-FDG PET/MRI (b) is visible, indicating an axillary lymph node metastasis. Accordingly, histopathology confirmed malignancy