Morphine and treatment of cancer -related pain-risk or benefit?

Morphine has been widely used to treat physical non-cancer pain as well as cancer-related pain. However, a growing body of evidence has emerged indicating that morphine in addition to alleviating pain initiates and suppresses immune functions in different types of cancer. At present the actions of morphine on tumor growth are contradictory with both inhibition and stimulation reported. Thus, the effects of morphine use needs to be identified with respect to the immune system in consideration of the therapeutic course to follow. It is known that cancer cells express various types of opioid receptors and morphine interaction with these receptors needs to be elucidated in cancer treatment. The expression and distribution of different opioid receptors for morphine binding may provide a basis for varying effects attributed to morphine actions on cancer cell promotion and suppression. Evidence indicates that knowledge regarding distribution of opioid receptors may be considered as a therapeutic tool to determine the use of morphine as a painkiller to treat cancer-related pain.