Purpose. Сomparative analysis of the diagnostic efficacy of the radiopharmaceutical "99mТс - DARPinG3" in dosages of 1000, 2000 and 3000 μg for the diagnosis of breast cancer with HER2/neu overexpression in humans.

Material and methods. The study included 28 patients with breast cancer (T1-4N0-2M0) before systemic treatment: 13 – with HER2/neu overexpression; 15 – with negative expression. In all cases, morphological, immunohistochemical studies, as well as FISH analysis of the primary tumor were performed. All patients underwent radionuclide studies (planar scintigraphy and SPECT of chest) at 2, 4, 6 and 24 hours after injection of the "99mTc - DARPinG3" in dosages of 1000, 2000 and 3000 μg.

Results. The half-life of the labeled protein from the blood was 3.5 hours for a dosage of 1000 μg; 3.8 h - for 2000 μg and 3.4 h – for 3000 μg. The effective dose for 1000 μg was 0.011 ± 0.001 mGy; for 2000 μg - 0.012 ± 0.006 mGy and for 3000 μg – 0.012±0.003 mGy. The liver absorption dose was significantly higher with 1000 μg of protein compared to 2000 and 3000 μg (p <0.005, Mann-Whitney U test). The tumor/background ratio was significantly higher at 2, 4 and 6 hours after injection of the 3000 μg «99mTc-DARPinG3» in patients with HER2-positive tumors (p <0.005, Mann-Whitney U test).

Conclusion. Clinical studies of the drug "99mTc - DARPinG3" at dosages of 1000, 2000 and 3000 μg demonstrated the rapid elimination from the bloodstream and its specificity for breast tumors with HER2/neu overexpression. The most important point of the work is the identification of a positive correlation of the protein dose with its accumulation in the liver, which was clearly demonstrated in comparison with 1000 and 3000 μg dose protein.