CAM stands for "complementary and alternative medicine". Complementary means complementary to conventional medicine and alternative likewise means an alternative to conventional medicine. No one should undertake either complementary or alternative therapies without consulting their doctor first, especially if they have a health condition, as even some natural and seemingly benign supplements can interfere with conventional treatments.
A whole industry has grown up to provide these treatments, and as the advances in medical treatments become ever more complex and less understood by patients, CAM offers simplistic 'remedies' that people can understand. Many CAM practitioners demonise conventional treatments to scare patients unnecessarily. Patients are often scared of the consequences of their disease and many seek reassurance that the conventional treatment will be less worse than the ailment. But because this may not be the case in the short term - chemo is horrible and no good doctor would ever minimise the side-effects it causes - they may be lured by the claims of the CAM practitioner who is under no compulsion to be as honest.
Remember the words of Tim Minchin (or possibly Dara O'Briain): 'Do you know what they call alternative medicine that has been proved to work? --- Medicine."