F-FDG-PET/CT for systemic staging of patients with newly diagnosed ER-positive and HER2-positive breast cancer.

Objectives: This study assesses F-FDG-PET/CT for patients with newly diagnosed estrogen receptor-positive/human epidermal growth factor receptor-negative (ER+/HER2-) and human epidermal growth factor receptor-positive (HER2+) breast cancer.

Methods: In this Institutional Review Board-approved retrospective study, our Healthcare Information System was screened for patients with ER+/HER2- and HER2+ breast cancer who underwent F-FDG-PET/CT prior to systemic or radiation therapy. The initial stage was determined from mammography, ultrasound, magnetic resonance imaging, and/or surgery.F-FDG-PET/CT was evaluated to identify unsuspected extra-axillary regional nodal and distant metastases. The proportion of patients upstaged overall and stratified by stage and receptor phenotypes was calculated along with confidence intervals (CI).

Results: A total of 238 patients with ER+/HER2- and 245 patients with HER2+ who met inclusion criteria were evaluated. For patients with ER+/HER2-breast cancer, F-FDG-PET/CT revealed unsuspected distant metastases in 3/71 (4%) initial stage IIA, 13/95 (14%) stage IIB, and 15/57 (26%) stage III. For patients with HER2+ breast cancer, F-FDG-PET/CT revealed unsuspected distant metastases in 3/72 (4%) initial stage IIA, 13/93 (14%) stage IIB, and 13/59 (22%) stage III. The overall upstaging rate for IIB was 14% (95% confidence interval (CI): 9-20%).

Conclusions: F-FDG-PET/CT revealed distant metastases in 14% (95% CI: 9-20%) of patients with stage IIB ER+/HER2- and HER2+ breast cancer, which is similar to upstaging rates previously seen in patients with stage IIB triple-negative breast cancer (15%, 95% CI: 9-24%). The detection of unsuspected distant metastases in these patients alters treatment and prognosis. NCCN guidelines should consider adding patients with stage IIB breast cancer for consideration of systemic staging with F-FDG-PET/CT at the time of initial diagnosis.