Essiac Extra Herbs, Amounts

If one decides to use the eight herb Essiac formula, the four potentiating herbs are added in 1 oz. increments each to the Rene Caisse original formula. The four potentiating herbs are: blessed thistle, kelp, red clover, and watercress.

These additions seem to come from the Dr. Brusch, Elaine Alexander, Flora Company (that makes Flor.Essence) camp. Dr. Brusch did indeed have a friendly association with Rene Caisse spanning many years and worked with him at his Massachusetts clinic.
It is not known what the exact circumstances were in developing the eight herb formula.

I have seen warnings that genistein, a plant estrogen, would not be good for anyone with hormone dependent tumors, including estrogen dependent mammary tumors, or prostate tumors.

Red clover does indeed contain the plant estrogen, genistein. There is still debate in the medical world concerning whether genistein is good for Breast Cancer patients or not. Genistein will lessen hot flashes, so there is an active estrogen in it.