Objective: Bone-specific radiotracers are known to accumulate in breast lesions. Tc-99m diphosphonates have been widely studied in differentiating breast lesions. In this retrospective study, we aimed to assess the uptake of the bone-specific PET radiotracer, F-18 fluoride (NaF), in primary breast cancers to determine its sensitivity and to identify any differences in NaF uptake between calcified and non-calcified tumors, histological subtypes, and patients with or without axillary lymphadenopathy.
Methods: NaF positron emission tomography/computed tomography (PET/CT) images of 69 newly diagnosed breast cancer patients were reviewed. F-18 fluoride uptake as maximum standardized uptake value (NaF SUVmax) was measured in the primary tumor, enlarged axillary lymph nodes and contralateral normal/non-tumoral breast tissue. Low-dose CT images were reviewed to locate the primary tumor and grossly assess its calcification and check for ipsilateral axillary lymphadenopathy. Whole body NaF PET/CT images were reviewed to search for bone metastases. Eighteen patients also underwent F-18 fluorodeoxyglucose (FDG) PET/CT study.
Results: The primary breast tumor was clearly seen as focal or diffuse uptake on NaF PET images in 27 of 69 patients (39%) (mean NaF SUVmax: 2.0 ± 1.0). In the rest, there was only mild bilateral diffuse breast uptake. When analyzing images per histological subtype (42 patients, 43 tumors), 14 of 31 invasive ductal carcinomas (IDC) (45%) and 3 of 4 ductal carcinoma in situ (DCIS) were visible on PET. Five invasive lobular carcinomas, 2 invasive mammary carcinomas, and 1 mucinous carcinoma were not visible on PET. Mean NaF SUVmax of contralateral normal/non-tumoral breast tissue was 1.0 ± 0.4. There was no significant difference in mean NaF SUVmax of primary tumor in cases with and without calcification or with and without axillary lymphadenopathy (p 0.892 and 0.957). There was no correlation between NaF SUVmax and FDG SUVmax values of the primary tumors (r 0.072, p 0.797, Pearson correlation).
Conclusion: NaF PET has relatively low sensitivity in detecting breast cancer. However, abnormal breast uptake on NaF PET requires further evaluation. F-18 fluoride uptake in the primary breast tumor does not seem to be correlated with axillary lymphadenopathy (metastasis potential), gross tumor calcification or metabolic activity of the tumor.
Keywords: Breast cancer; F-18 fluoride; NaF; PET/CT; Primary breast tumor.