Essiac tea is not recommended as a standalone treatment for cancer. It is a good overall tonic and is good for cleansing but is now considered a fairly weak cancer treatment that is best used in combination with other more potent cancer fighting and immune boostiing elements.
When Rene Caisse had her successes and the early users of essiac tea had success, the nutrients in our food were much greater and the additives much less. Also there was much less carcinogens and other chemical compounds in the air we breathe, food we eat and water we drink.
There are a lot of protocols and cancer fighting elements that may have worked for one person or for a few people - the best plan is to find one that has worked for a large majority of people. Essiac certainly no longer fits that description, though, as I mentioned, it would be a good item to include in a stronger and more effective overall protocol.