Sorry to hear about your symptoms. Unfortunately, Vincristine is well known to cause pretty severe PNs. Don't know what you;ve tried but I can give you a list of things that we used here. First, capsaicin cream (over the counter) burns when you initially apply it, but is supposed to "burn out" the pain fibers giving you some relief. Lidocaine patches and combo ketoprofen/ketamine patches have also been helpful to some patients. Seizure meds: tegretol, neurontin, gabatril,topamax, dilantin, depakote, trileptal have been successful in some people. Elavil and prednisone (lots of side effects) are other possibilities. Biofeedback.
Now this may sound a little crazy, but it's cheap, has no side effects, and one of our patients with post herpetic neuralgia (a very painful condition associated with shingles) is actually pain free with this. I think he was either a carpenter or engineer who accidentally discovered that putting a small sandpaper disk (just a circular disk that he cut from an optimum grade of sandpaper) against the area somehow ??stimulated the pain fibers or anesthetized them. Not sure, but he swears by it.
Hope that helps