In traditional Chinese medicine, onions are said to enhance chi or energy. They induce urination and perspiration. It is recommended for consumption when the weather is cold. Mixed with garlic and sugar, onion is said to lessen respiratory stress caused by cold weather.
Herbal medicine systems of both China and India regard onion as beneficial to the cardiovascular system. It helps reduce blood platelet aggregation and cholesterol levels. WHO (World Health Organization) supports onions to treat appetite loss and prevent atherosclerosis (hardening of arteries).
The anti-cancer property of onion has been studied by Votto et al. (2010). Their experiments showed that cell death occurs when exposed to onion extract due to damage caused to the DNA.
The plant is rich in antioxidants, flavonoids, and phenolic compounds.
I have researched the major herbs used in Ayurveda and TCM to treat cancer. Onion is not listed as an anticancer herb in these formulations.