Whilst I am NOT making any claims here, there are some herbs that have been used to support a horse with cancer. Many of them have undergone studies.
Wormwood has had quite a few studies done on it’s effectiveness with cancer.
Aloe vera is another herb that is being studied for it’s benefits with cancer. One of my clients put aloe daily on a cancerous growth around the edge of her horse’s nose and after a few weeks it had totally disappeared.
Some other things that have been studied to help with cancer are; blackberries, bloodroot (for skin cancer), burdock root, cascara (bowel cancer), chamomile, chaparral, clove, maritime pinebark, echinacea (skin cancer) gentian (melanoma, thyroid and lymphoma), ginger (ovarian and colon), graviola and grape seed extract. Herbs are not to be used to replace veterinary advice.
Other things to consider are a good quality natural mineral supplement such as a good quality kelp, bladderwrack or nori. Keep your horse on a natural diet with unprocessed foods and minimize the amount of chemicals that your horse is exposed to.