They couldn't deal with the toxins produced back then.
Actually blowing up Cancer cells is never a good idea, therefore Iodine and selenium are a must and much better to use the Retro-Viruses and let the body deal with it through Apoptosis vs Necrosis.
Then I have no experience with large Tumors only the incidental ones we get from Metal detox...
Also we know that the Blood Cleaner will help if Necrosis is an issue...