Paul McCartney has said he will stop funding cancer research charities that use animals:

he revealed plans to refuse funding to organisations that practice vivisection, after discovering a number of charities close to his heart advocate the practice

It’s quite right that he follows his own beliefs but not that he uses his celebrity to spread untruths:

There are better alternatives but you’re not allowed to challenge the status quo

This is just not true:

A great deal of cancer research is carried out without using animals. In certain areas, however, animal research remains essential if we are to understand, prevent and cure cancer. (Cancer Research UK)

So where does he get his information? Apparently from Alistair Currie - Senior Research and Campaigns Co-ordinator - People for the Ethical Treatment of Animals. So we know why he is so misguided.