I am simply copying pasting Sara Anne's response a few weeks ago as it is a pretty concise summary. It IS a good product especially with BCG being in short supply.
When mitomycin is used in this way it really is not being used as a chemotherapeutic agent. Its purpose is the same as BCG. That is to stimulate your immune system to reject the cancer cells in the bladder. Since there is currently a shortage and BCG is hard to obtain, your urologist is using mitomycin in the same way, as an immune system stimulant, NOT as a chemo agent. It will be instilled into your bladder directly. You may have some side effects but it will be nothing compared to receiving chemo.
And remember...you do have friends and support here,
DX 5/6/2008 TAG3 papillary tumor .5 CM in size. 2 TURBS followed by 6 instillations of BCG weekly with a second round of 6 after a 6 week wait.