Have you ever seen a patient spontaneously become cured from cancers without treatment?

Even if happens: It is not an excuse to avoid treatment(s) , best chances for cure is early detection , taking proven treatments , not to wait for rare spontaneous regression of cancer

Not Really: People may get small cancers that are destroyed by the immune system. These people are never even diagnosed in the first place. Once a tumor has grown enough to be detected it has "learned" to evade the immune system and spontaneous remissions are very rare. I have seen patients in which the immune system killed the primary tumor, some cells survived, spread to other organs, and grew into tumors.