I am not a doctor and I don't know yours credentials, however most doctors have little or no training in nutrition. You oncologist may have more because chemotherapy also radically damages the immune system. Your blood count will continue to get worse while you take it.
I had stage II muscle invasive bladder cancer. My oncologist did not support my supplementation, but did not prohibit it.. I had 4 split sessions of Gemcitabin/Cisplatin over 5 months. I declined preliminary steroids which damage the immune system. . Before, during and after I was taking one gram doses of both curcumin and "timed release" C about every 4 hours. Also some A, E, D, Selenium and Papaya enzyme to help build platelets . No side effects at all. Now cancer free and on one gram doses twice daily for maintenence.
Be very careful with supplements that are not water suluble as concentrations can become toxic. Most doctors have reasured me that B and C vitamins as well as curcumin will not hurt you because they are flushed from your body in hours.