FDG PET not equally valuable for systemic staging of all breast cancer histologies

A recent study has shown that FDG PET/CT, while useful for systemic staging of stage III ductal breast cancer, adds little to the systemic staging of invasive lobular breast cancer (ILC).

The findings, presented at the ARRS 2015 Annual Meeting in Toronto, may signal a need to modify National Comprehensive Cancer Network (NCCN) guidelines that consider FDG PET/CT appropriate for systemic staging of newly diagnosed stage III breast cancer.

“We are evaluating patient and disease factors that affect the value of FDG PET/CT for systemic staging of locally advanced breast cancer,” said study coauthor Molly Parsons, MD, of New York Presbyterian Hospital-Weill Cornell Medical Center and Memorial Sloan Kettering Cancer Center, in a press release. “Our ongoing work suggests that the histology of the primary breast malignancy may be one such factor.”

Parsons and colleagues retrospectively screened their institution’s record for patients with ILC who underwent PET/CT from 2006 to 2010 prior to being treated with chemotherapy, hormonal therapy or radiation. A total of 146 patients fulfilled the study’s inclusion criteria and the relevant PET/CT studies were reinterpreted by a radiologist experienced with PET/CT.

Results showed that PET/CT did not reveal unsuspected local extraaxillary nodes in any patient and no unsuspected distant metastases in the eight patients with an initial stage I diagnosis. PET/CT did reveal unsuspected distant metastases in two of 50 initial stage II patients and 10 of 88 initial stage III ILC cases.

However, Parsons and colleagues noted that nine of these 12 upstaged patients would have also been upstage by CT, bone scan or both and two of the 12 were upstage by the CT component of the hybrid scan, as they had sclerotic osseous lesions that were not FDG avid.

False-positive FDG PET findings led to unnecessary further tests in two patients.

The authors concluded that at best, only 3 percent of patients with newly diagnosed stage III ILC breast cancer would have benefited from systemic FDG PET/CT staging, as opposed to conventional CT and bone scanning.

“Future NCCN guidelines for systemic staging of breast cancer may need to be modified to consider the histologic subtype of the breast malignancy, with ILC staged with CT and bone scan rather than FDG PET/CT,” wrote the authors.