I have just read Professor Plant's book and it seems to have a strong ring of truth about it!
As a retired family doctor who did two baby clinics a week for 30 years, I found it not uncommon for breast-feeding mothers to switch to the bottle saying that their babies grew better. Gradually, I came to suspect that growth was excessive, not better. Babies triple their weight in the first year of live, calves about a dozen-fold. There seems to be a correlation between growth factor in milk, and cows milk contains more than mother's milk and this factor stimulates breast and prostate gland growth.
Six years ago my brother-in-law, then aged 72 years, developed prostate cancer with bone secondaries. At my suggestion he promptly went vegan (though later he added fish twice a week making a 'macro-biotic like' diet. Although he also received hormone therapy, the surgeon initially felt he had made an error in diagnosis because the secondaries in the bones vanished so rapidly. However his PSA rapidly dropped from 211 to under 1!
This, and other clinical experiences over many years suggested to me a relationship between diet and cancer, especially some animal products but milk in particular. Milk is designed as an interim food, from birth until weaning and cow's milk is for calves. (There is an argument for 'formula' if mother cannot breast-feed). Cow's milk derives from various grasses, and similar nutrients are found in the green-leafy vegetation which people eat. Dairy products are irrelevant to the human diet. I feel it wiser to restrict or avoid dairy foods until proved safe and healthy to eat.