You are there for your wife. She is there for you. The doctor who oversees my hormone replacement therapy is herself and fully-transitioned, male-to-female transsexual who, by the way, owns the medical practice at which many doctors practice. She told me:
People marry a person and not a set of genitals.
If only real life were actually that simple, huh? However, her point is valid. Granted, your wife and you may not necessarily be able to continue as traditional spouses, but you CAN be the very best of friends. That's what my wife and I have become.
Cancer? Be her rock of support, and she'll truly appreciate it. I wish you the very best in your quest and in your circumstances.