PET/CT-MRI for staging of breast cancer patients: Preliminary experience

Objectives The aim of this pilot study was to assess the diagnostic efficacy for the staging of breast cancer using the co-registration of PET/CT and MRI.

Methods Thirty-five breast cancer patients were included. Clinical staging included breast ultrasonography was preceded. All patients underwent whole body FDG PET/CT, breast MRI, and delayed breast PET/CT sequentially in prone position. Breast MRI consisted of T2, diffusion weighted image (DWI), and dynamic Gd-DTPA enhanced MRI. Each tumor was characterized by 5 parameters: maximum SUV at early PET scan (SUV1), maximum SUV at delayed PET scan (SUV2), change of maxSUV (ΔSUV), longest size at MRI, and apparent diffusion coefficient (ADC). The pattern of enhanced curve was also evaluated.

Results Stage changed after PET/CT-MRI in 24 patients (68.5%): upstaging in 12 and downstaging in other 12. In 7 patients, distant metastases unknown initially were found by whole body PET/CT. MRI found more number of small sized axillary nodes than PET/CT. Fifty-three breast tumors were evaluated in 35 patients. The mean and SD of parameters were SUV1: 5.7±3.9, SUV2: 6.3±4.4, ΔSUV: 9.6±14.8%, size: 23±16 mm, and ADC: 1.17±0.3, respectively. ADC showed negative correlation with SUV1 (r=-0.2707, p=0.0499), SUV2 (r=-0.2994, p=0.0294), and ΔSUV (r=-0.3380, p=0.0133). ADC was independent of size, while SUV showed size dependency. Nine tumors were considered false negative on PET (SUV1 < 2.5). Three of them showed ADC < 1.1 and 4 of remains showed washout or plateau enhancing pattern, so were reclassified as true positive.

Conclusions FDG PET/CT and MRI were complementary in staging of breast cancer and characterizing tumor. Functional MRI was useful in PET false negative tumors. Further study about the role of whole body PET-MRI fusion image is needed