Our group has previously reported potential new radiopharmaceuticals, i.e. 99m Tc-tricarbonyl-(2-amino- 5,10-dioxide- 7(8)-fluorophenazine), Tc-FZ), with the ability to detect hypoxic tumoral tissues. Previously, this probe was used to detect solid tumors, employing a model of lung carcinoma generated by inoculation of 3LL Lewis murine cells in C57BL/6 mice. The results
revealed an adequate tumor/muscle ratio, 3.8 at 2 h post-injection (p.i.), with lower tumor/blood ratio, i.e. 0.6 at 2 h p.i..

Due to some models of breast cancer also being characterized by hypoxic areas, herein we decided to analyze the behavior of Tc-FZ in BALB/c mice bearing mammary tumor induced with 4T1-mouse tumoral cell line. The studied ratios revealed to be slightly a little more unfavorable than in the lung tumor-porting animals, being tumor/muscle and tumor/blood ratios, at 2 h p.i., of 3.0 and 0.23, respectively. Additionally, animals in vivo images showed that the liver masked tumor signal.

Acknowledgement
The authors want to thank the ANII for financial support.