Most of the cell lines (including human) works successfully if you inject in specific mouse models which are immuno-deficient like nude mice or scid mice. I personally have experience in inducing human glioblastoma cell line in those mice and tumour was grown successfully.

Sorry, I forgot to mention about the cell concentration. Actually for growing tumour in usual flank region we injected 100000 cells. But I found intracranial injection of 30000 cells are enough to induce tumour in brain.