Hi, firstly, can I offer you my support in facing this horrible disease. I have had a brush with cancer myself so I know the mental turmoil that it caused me. Please don't let guilt and mental programming make it worse. One thing WT has right is that we are all imperfect. Nobody has a right to expect perfection from you even in holding to discredited mores. Don't expect it from yourself.
I have trained myself by eating black (blood) pudding. Nothing terrible happened, it was quite an unremarkable experience despite the clanging of taboos in my head.
This issue is very close to me since I have had two family members die as a direct consequence of this doctrine so the eating of blood had great symbolic resonance to me. This act of rebellion helped me free myself of the guilt and weight of expectation that I carried for decades. Having undergone operations recently I have discussed the blood issue and my (none) stance with surgeons and other staff explaining the threat of shunning if I willingly received blood.
Don't be held by that threat.