Potential of targeted GRPR imaging for the detection of bone metastases in patients with luminal breast cancer

Background. Luminal breast cancer, comprising 60–80 % of cases, is characterized by a high frequency of bone metastasis, necessitating continuous surveillance for early detection of distant metastases. Traditional imaging methods have limited sensitivity, especially for small lesions. Therefore, the development of highly sensitive methods for early diagnosis is relevant. Targeted radionuclide imaging of the gastrin-releasing peptide receptor (GRPR) using antagonist-based radiopharmaceuticals, such as [^99ᵐTc]Tc-DB8 is a promising non-invasive method for detecting small lesions.
The aim of the study was to demonstrate the potential of [^99ᵐTc]Tc-DB8 for detecting bone metastases in patients with luminal breast cancer.
Case report 1. A 51- year-old woman diagnosed with stage IIIC right breast cancer (T2N3M0), with multicentric growth, metastatic involvement of the axillary and subclavian lymph nodes, underwent SPECT/CT 2 hours after the intravenous administration of [^99ᵐTc]Tc-DB8 at a protein dose of 80 μg. The detection of a high-uptake [^99ᵐTc]Tc-DB8 lesion in the right 5th rib, confrmed as a lytic bone destruction on CT, indicated a high suspicion of bone metastasis. Followup chest CT showed an area of uneven sclerotic changes, interpreted as a response to therapy.
Case report 2. A 42-year-old woman was diagnosed with stage IV right breast cancer (T1N1M1), metastatic involvement of the axillary lymph node, and multiple bone metastases. A SPECT/CT performed 2 hours after the intravenous injection of [^99ᵐTc]Tc-DB8 at a dose of 80 μg revealed high uptake of the radiopharmaceutical in the primary tumor, metastatic lymph nodes, and extensive bone metastases. Specifcally, the radiopharmaceutical accumulated in the L2-S2 vertebrae, the right ilium and ischium, and the posterior segment of the 7th rib on the right, identifying these as metastatic sites.
Conclusion. Results of the clinical study on [^99ᵐTc]Tc-DB8 demonstrated its high effcacy in detecting bone metastases in patients with luminal breast cancer.

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