Prospective comparison of CT and 18F-FDG PET/MRI in N and M staging of primary breast cancer patients: Initial results

Abstract

Objectives: To compare the diagnostic accuracy of contrast-enhanced thoraco-abdominal computed tomography and whole-body 18F-FDG PET/MRI in N and M staging in newly diagnosed, histopathological proven breast cancer.

Material and methods: A total of 80 consecutive women with newly diagnosed and histopathologically confirmed breast cancer were enrolled in this prospective study. Following inclusion criteria had to be fulfilled: (1) newly diagnosed, treatment-naive T2-tumor or higher T-stage or (2) newly diagnosed, treatment-naive triple-negative tumor of every size or (3) newly diagnosed, treatment-naive tumor with molecular high risk (T1c, Ki67 >14%, HER2neu over-expression, G3). All patients underwent a thoraco-abdominal ceCT and a whole-body 18F-FDG PET/MRI. All datasets were evaluated by two experienced radiologists in hybrid imaging regarding suspect lesion count, localization, categorization and diagnostic confidence. Images were interpreted in random order with a reading gap of at least 4 weeks to avoid recognition bias. Histopathological results as well as follow-up imaging served as reference standard. Differences in staging accuracy were assessed using Mc Nemars chi2 test.

Results: CT rated the N stage correctly in 64 of 80 (80%, 95% CI:70.0-87.3) patients with a sensitivity of 61.5% (CI:45.9-75.1), a specificity of 97.6% (CI:87.4-99.6), a PPV of 96% (CI:80.5-99.3), and a NPV of 72.7% (CI:59.8-82.7). Compared to this, 18F-FDG PET/MRI determined the N stage correctly in 71 of 80 (88.75%, CI:80.0-94.0) patients with a sensitivity of 82.1% (CI:67.3-91.0), a specificity of 95.1% (CI:83.9-98.7), a PPV of 94.1% (CI:80.9-98.4) and a NPV of 84.8% (CI:71.8-92.4). Differences in sensitivities were statistically significant (difference 20.6%, CI:-0.02-40.9; p = 0.008). Distant metastases were present in 7/80 patients (8.75%). 18 F-FDG PET/MRI detected all of the histopathological proven metastases without any false-positive findings, while 3 patients with bone metastases were missed in CT (sensitivity 57.1%, specificity 95.9%). Additionally, CT presented false-positive findings in 3 patients.

Conclusion: 18F-FDG PET/MRI has a high diagnostic potential and outperforms CT in assessing the N and M stage in patients with primary breast cancer.

Fig 1. Determination of the lymph node stage in CT (A) and ¹⁸F-FDG PET/MRI (B).

Fig 2. A 45-year old woman with diagnosis of primary breast cancer.

No distant metastases were detected in the CT scan (a). The subsequently performed ¹⁸F-FDG PET/MRI shows a bone metastasis in the left iliac bone with contrast enhancement on T1w fs VIBE (c) and pathological FDG uptake on PET (d) and fused ¹⁸F-FDG PET/MRI (b).

Fig 3. A 48-year old woman with diagnosis of primary breast cancer.

Morphologically unsuspicious right axillary lymph node rated as not malignant in the CT scan (a). The ¹⁸F-FDG PET/MRI shows a slight FDG uptake (b-d), indicating malignancy. Histopathology proved a tumor infestation.

Fig 4. A 72-year old woman with diagnosis of primary breast cancer and lymph node metastases.

The reading radiologist did not detect the morphologically inconspicuous left clavicular lymph node in CT scan (a). In ¹⁸F-FDG PET/MRI a clear FDG uptake is visible (b-d). Histopathology confirmed malignancy.