Locoregional staging of locally advanced luminal-like lobular breast cancer: First descriptive case series comparing prone [¹⁸F]FACBC PET/CT and breast MRI

Background: The second most common breast cancer subtype is invasive lobular cancer (ILC). Its locoregional staging is challenging, even when using breast MRI. Different non-[¹⁸F]FDG PET tracers have been explored in these patients, and promising results were reported with [¹⁸F]FACBC. Nevertheless, no publications directly comparing breast MRI and [¹⁸F]FACBC PET are available.

Aim: To compare the performance of prone [¹⁸F]FACBC PET/CT and breast MRI for assessing disease extent in the breast and for depicting lymph node metastases in patients with locally advanced ILC.

Methods: Retrospective selection of case series of patients with proven locally advanced luminal-like ILC, who underwent both breast MRI and prone [¹⁸F]FACBC PET/CT, according to the local clinical standards.

Results: Eight patients were included. [¹⁸F]FACBC PET/CT performed similarly to MRI in T-staging and outperformed MRI in N-staging, especially outside axillary level I/II. [¹⁸F]FACBC uptake in the index breast lesion was on average 9 times higher than the breast background. Among the 6 patients submitted to surgery, [¹⁸F]FACBC provided the correct T&N staging in 5 patients, confirmed by pathology.

Conclusion: This initial descriptive case series suggests that prone [¹⁸F]FACBC PET/CT could be a valuable imaging tool for both local and regional staging of low-grade luminal-like ILC. A larger prospective clinical trial is needed to further evaluate this potential application.