Morphine and cancer progression: hydrogen peroxide points to need for more research.

Background: Morphine is widely used in the management of intractable cancer pain. However, conflicting views exist on two suspected nonanalgesic properties of morphine: suppression of immune function and inhibition of cancer progression.

Methods: In vitro measurement of the tumor growth-inhibiting signaling molecule, hydrogen peroxide (H2O2), released from the cultured acute monocytic leukemia cell line, THP-1, in the presence or absence of morphine.

Results: Morphine at concentrations of 10(-8) M significantly reduced H2O2 release from THP-1 cells.

Conclusions: These results provide a proof of concept for morphine's ability to inhibit H2O2 production and release in a leukemia cell system and point to a possible and as yet unrecognized tumor-promoting effect of morphine. More research is needed to systematically examine this suspected morphine-associated tumor-promoting effect.