I'm curious as to how fast does kidney cancer grow?

It's hard to say: Kidney cancer, also called renal cell carcinoma, is increasing in incidence. In a study where patients were followed by imaging after diagnosis, growth rates were very different. Tumors that had not spread grew at 0.1 to 1.35cm per year. Tumors that were metastatic grew faster, up to 7cm per year. It varies for each person and for each tumor.