I saw a good analysis of it (including the relative amounts of material in the common formulas and the impact on the human body:
www.ompress.com...
The conclusion was:

ssiac-like formulas have no proven anticancer effect in humans or animals but nonetheless remain popular as alternative
treatments. Based on a simplistic analysis of the amount of herbal material and active constituents in these formulas, it seems unlikely that they
would produce any significant medical effect, other than a slight purgative action. The purgative action could be of general benefit to some
individuals, but would also prevent significantly higher doses of the formula from being used in cancer treatment. Because of the popularity of
Essiac-like formulas, adequate assessment of their anticancer potential is needed.

Now... in folk medicine, things that make you throw up or go to the bathroom are given unusual weight as "effective cures" because they are
"purging the bad stuff" from your body. But there's too little of the various types of compounds to do much of anything ot the body.
I think it could give some emotional support or mild immune system support when other treatments are used, but I'd not risk my life on that formula.
And the "suppressed by scientists" is a usual claim by people who are selling ineffective materials.
I'd stick with standard treatments, myself.