I have recently been injecting various tumoral cell strains through the mouse tail vein. However, I had some evidence of a local tumor seeding approximately one inch above the injection site. I usually try to flash wash the injecting catheter with 100 uL sterile PBS after the tumoral cells, but it seems like the cells precipitate and seed a few inches above. This phenomenon happens in addition to distance metastasis, which is favorable to me. However, I do not like my mice to have concurrent tail tumors, which can hasten their death. Does anyone have the same experience? I would appreciate it if you could help me find a solution. I am 99 % sure that I had injected IV as I always have the blood backflow through my catheter, and also, while injecting the cells, there is no backpressure.

Thanks,

Haneyeh