Prospective study on ¹⁸F-FDG PET-CT for staging locally advanced invasive lobular breast carcinoma

Patients with locally advanced breast cancer (LABC) undergo staging tests. In the absence of metastases, they may receive combined modality therapy with curative intent. A randomised controlled trial (RCT) in patients with locally advanced breast cancer (LABC) compared staging using 18F-FDG PET-CT versus the usual CT chest/abdomen and bone scan, with the primary outcome being upstaging to Stage 4. Because of concern regarding the lower FDG-avidity of invasive lobular breast cancer (ILBC) compared to invasive ductal cancer (IDC), patients with ILBC were not eligible for the RCT.

A prospective cohort study in patients with ILBC and TNM stage III or IIb (T3N0) was conducted contemporaneously to the RCT. Consenting patients from six regional cancer centres in Ontario all underwent whole body 18F-FDG PET-CT, CT with contrast of the chest/abdomen, and a bone scan. The primary endpoint was upstaging to stage IV. (ClinicalTrials.gov identifier: NCT02751710).

Between December 2016 and April 2022, 41 patients with ILBC were enroled: 38 undergoing all three imaging tests. Five patients (13.2%) were upstaged due to distant disease; all had positive PET-CT scans. Among these five patients, two were positive on both CT and bone scan, two on either CT or bone scan, and one on neither. Six of 38 (15.8%) primary ILBC tumours lacked ¹⁸FDG uptake and the mean standard uptake value was 4.4 (3.2).

In this cohort, 18F-FDG PET-CT detected all cases of metastatic spread.