In Esoteric Medicine and Practical Magic, Samael Aun Weor wrote several important chapters about cancer, which I have linked below.
Obviously, this is a serious karma, but there are antidotes you can apply, as given in the articles.
I have observed that the rattlesnake medicine is very powerful. Be aware that it purges the illness in a rigorous way, and the patient can experience strong nausea. I believe this is far more acceptable than the side effects of chemotherapy, etc.
The transmutation practices will aid in your healing, so it is important that you use them in your fight to get better.
Appeal constantly to your Divine Mother for help.
Remember: we need to pay our karma, thus it is wise to perform superior actions so that the inferior debts are overcome. The stronger and more difficult our debts, the greater our sacrifices and efforts must be.