Hi all - looking for some advice on a preliminary study of tumor growth. I am doing a study with ten NOD/SCID mice. All mice have a 0.72 mg pellet of estrogen inserted between their shoulder blades, and after two days they received a xenotransplant of 5 x 10^6 MCF-7 cells with an inducible plasmid.
An aside about the cells - they were cultured normally, treated with trypsin, centrifuged down, washed and resuspended in sterile phosphate-buffered saline. They were counted using a hemocytometer, and the concentration was adjusted to that they were the correct concentration in 200 microliters of PBS. This solution was then inserted subcutaneously into the left flank of the mice I described above.
The issue is that a month later, there's no tumor growth observed. This is the second time I've attempted this protocol, but the first was with RAG-knockout mice, who also did not develop tumors (although they did get an inflamed uterus).
Did I do something wrong?