Opioids may promote tumours

OPIOIDS given to reduce pain in cancer patients may actually promote tumour growth and metastasis, two studies suggest.

In one study, based at the University of Chicago, overexpression of opioid receptors in a lung cancer cell line increased in vitro and in vivo measures of tumour growth and metastasis. 

In another study, based at the University of North Carolina at Chapel Hill, naturally occurring genetic differences in opioid receptor biology correlated to breast cancer survival in a cohort of more than 2000 women. 

Breast cancer mortality was significantly reduced (at least halved) in patients with a genetic variant in the opioid receptor that reduces opioid response. 

Several studies have shown a reduced incidence of cancer recurrence after reduced doses of opioids post-surgery for breast, prostate and colon cancer and melanoma, although others have not detected any significant differences, the authors of the lung cancer study noted. 

They said their results implicated opioids in these epidemiological findings. 

But Melbourne Health anaesthetist Dr Malcolm Hogg, president elect of the Australian Pain Society, called that “a big jump”.

He said that while it was important to be aware of the link, other factors likely contributed to the outcomes. 

“Whilst opioids themselves appear to inhibit immune cell function in the laboratory, we also know that poorly controlled pain impairs immune function,” Dr Hogg said. “So removing opioids and having poorly controlled pain could potentially be just as detrimental.

“When you’ve got less pain, you’ve got less stress reaction, and so we believe the immune system functions better.”

He said patients should be given a combination of simple analgesics such as paracetamol and anti-inflammatories – along with nerve-modulating medication to improve pain control. 

“This can have the effect of limiting reliance and dosage levels of opioids, but opioids should not be excluded.”

Anesthesiology 2012; 116:857-67;896-902