Horse chestnut , also known as Aresculus hippocastanum is basically used in botanical medicine to treat venous disorders. I have used the herb and homeopathic preparations for hemorrhoids ( which are dilated veins) in many patients. In Europe it has bene used for venous condition as thrombophlebitis, varicose veins and even edema.
There is an active ingredient in Horse chestnut. It is a saponin called escin. There are other active components in Horse chestnut as flavinoid and esculin.
I would not consider Horse chestnut as an anti cancer herb. There was one in vitro study that found that horse chestnut saponins are cytotoxic to cancer cells., It can protect the vasculature and the surrounding edema.
This is yet another example of a herb beneficial effect in cancer therapy. It should be added to the armentarium of natural compounds.