An Approach to Breast Cancer Diagnosis via PET Imaging of Microcalcifications Using ¹⁸F-NaF

Abstract

Rationale Current radiological methods for diagnosing breast cancer detect specific morphological features of solid tumors and/or any associated calcium deposits. These deposits originate from an early molecular microcalcification process which consists of two types: type 1 is calcium oxylate (CO) and type II is carbonated calcium hydroxyapetite (HAP). Type I microcalcifications are mainly associated with benign tumors while type II have been shown to be produced, internally, by malignant cells. No current non-invasive in vivo techniques are available for detecting intratumoral microcalcifications. Such a technique would have a significant impact on breast cancer diagnosis and prognosis in preclinical and clinical settings. 18F-NaF PET has been solely used for bone imaging by targeting the bone HAP. In this work, we provide preliminary evidence that 18F-NaF PET imaging can be used to detect breast cancer by targeting the HAP lattice within the tumor microenvironment with high specificity and soft-tissue contrast-to-background ratio, while delineating tumors from inflammation. METHODS Mice were injected with approximately 106 MDA-MB-231 cells subcutaneously and imaged with 18F-NaF PET/CT in a 120 min dynamic sequence when the tumors reached a size of ~250 mm3. Regions-of-interest (ROIs) were drawn around the tumor, muscle, and bone. The concentration of the radiotracer within those ROIs were compared to one another. For comparison to inflammation, rats with inflammatory paws were subjected to 18F-NaF PET imaging. RESULTS Tumor uptake of 18F− was significantly higher (p<0.05) than muscle uptake where the tumor-to-muscle ratio was ~3.5. The presence of type II microcalcification in the MDA-MB-231 cell line was confirmed histologically using alizarin red S and von Kossa staining as well as Raman microspectroscopy. No uptake of 18F− was observed in the rat inflamed tissue. Lack of HAP in the inflamed tissue was verified histologically. CONCLUSIONS This study provides preliminary evidence suggesting that specific targeting of the HAP within the tumor microenvironment with 18F may be able to distinguishing between inflammation and cancer.

Detection of breast cancer microcalcification using 99mTc-MDP SPECT or Osteosense 750EX FMT imaging

“…3), we believe that it is mainly the presence of HAP that contributed to the observation of the uptake of 99m Tc-MDP in the tumor, similar to the mechanisms of bone uptake of this radiotracer. In contrast, we did not observe liver uptake of 18 F − since no HAP exists in the normal liver [19]. In the clinic, since the breast is relatively far from the liver, especially when using dedicated SPECT scanners, and since the radiotracer concentration in normal muscle tissue is significantly lower than that of tumor (please see Figs.…”

“…In Table 1, we compare the three different methods: 18 F-NaF PET (from our previous study [19]), 99m Tc-MDP SPECT, and Osteosense 750EX FMT for HAP imaging in breast cancer. Although the tumor to muscle ratio in the SPECT data (44.4 ± 40.3) was higher than that of the PET data (3.6 ± 1.4), this difference was not significant ( p > 0.05) due to the large error bars on the SPECT ratio.…”

“…The mouse models were created as described in previous work [19]. Briefly, the MDA-MB-231 cells were cultured in Dulbecco's Modified Eagle's Medium (DMEM, Invitrogen, Carlsbad, CA) supplemented with 10% fetal bovine serum and 1% penicillin streptomycin (Invitrogen, Carlsbad, CA) at 37 °C in a humidified, 5% CO 2 incubator.…”

“…We have previously reported on the presence of HAP in the MDA-MB-231 triple negative breast cell line and provided evidence for the use of 18 F-NaF positron emission tomography (PET) imaging for detecting MDA-MB-231 tumors in mouse models [19]. Upon administration, 18 F − dissociates from the sodium ion in the blood and binds to HAP within the tumor microenvironment in a manner similar to bone uptake.…”

Evolving Role of Molecular Imaging with 18F-Sodium Fluoride PET as a Biomarker for Calcium Metabolism

“…This application of PET would be the first noninvasive technique to detect intratumoral microcalcifications, greatly affecting the diagnosis and prognosis of breast cancer. Preliminary evidence already suggests that NaF-PET is able to differentiate between cancer and inflammation [76].…”