Bone is a common metastatic site for prostate and breast cancer, and bone cancer is usually associated with severe pain. But an increasing number of patients seek alternative therapies because of the failure of traditional treatments or their resulting side effects.

The researchers from the Johns Hopkins University School of Medicine in the US compared the analgesic effects of a diet with either soy or casein as a protein source on three experimental mice models of bone cancer pain.

They report some areas where soy appeared to reduce sensitivity to pain, such as in the femur model, although it had no effect on primary mechanical hyperalgesia (pain sensitivity) in the calcaneus model or on movement-related hyperalgesia in the humerus model.

"The study raises the possibility of dietary supplements influencing aspects of cancer pain. Further research will help determine if use of nutritional supplements, such as soy proteins, can reduce opioid analgesic use in chronic pain states and help minimize the side effects associated with long-term use of opioids," write the researchers in a recent issue of the Journal of Pain (5(2):104-110).

The soy diet had no impact on tumour size, bone destruction, and body weight in the femur model, suggesting that it had no effect on cancer growth.