- Morphine 'might spread cancer' (BBC News)
- Morphine May Help Tumors Spread in Cancer Patients (US News and World Reports)
- Pain drug morphine may accelerate cancer growth (Reuters, ABC News)
- Common Pain Relief Medication May Encourage Cancer Growth (Science Daily)
What about the claim that there is “mounting clinical evidence” that morphine may accelerate cancer growth? The only real clinical studies in this regard come from a single institution in Ireland and are basically a couple retrospective cohort studies comparing regional versus general anesthesia. The first one of these articles (Anesthesiology. 2006; 105(4):660-4) showed a beneficial relation between paravertebral block and cancer recurrence in women undergoing breast cancer surgery. The study’s authors acknowledge that “selection bias and the effects of unmeasured confounding variables” could not be excluded, as well as the fact that “relevant information such as the amount of morphine given” was not available in the records. The second study was nearly identical except it was in patients undergoing radical prostate surgery (Anesthesiology. 2008;109(2):180-7)
The most important take home point is that none of these studies actually looked at opioid use (although many of the news articles vaguely cite these studies as evidence for morphine’s deleterious effects on cancer). Even if you want to argue that these were high quality studies and there is a clear benefit of regional anesthesia, opioids should not be singled out as the cause. Benefit of regional anesthesia may be due to a myriad of other effects of regional anesthesia including the lack of volatile anesthetic agents or an improved stress response. These studies are noteworthy, but I agree with the authors of these articles that they should “be viewed as generating a hypothesis and an estimated effect size for future large randomized controlled trials”.
So if you have a patient on morphine asking you whether “morphine will make my cancer worse”, the answer is no. There is no clinical evidence that morphine, or any other opioids, cause real harm through stimulating cancer growth. There is though significant high quality evidence for their benefit in relieving pain and suffering.
Biki B, Mascha E, Moriarty DC, Fitzpatrick JM, Sessler DI, & Buggy DJ (2008). Anesthetic technique for radical prostatectomy surgery affects cancer recurrence: a retrospective analysis. Anesthesiology, 109 (2), 180-7 PMID: 18648226