Morphine has been shown to increase the proliferation and migration of breast cancer cells, as well as promoting angiogenesis (new tumor blood vessel formation). Morphine also suppresses the immune system. Animal and human studies comparing surgery with and without opiates such as morphine have found that use of opiates increases the likelihood of breast cancer recurrence. Now a new study has reported that while morphine does not appear to play a role in initiating breast cancer, it promotes the growth of existing tumors.

Morphine and breast cancer surgery

Surgery is an essential and effective treatment for breast cancer, assuming it is feasible. However, the stress response induced by surgery impairs immune system functioning and increases inflammation. In fact, surgery appears to promote metastasis through its effects on remaining breast tissue and even on tumor cells already located in other parts of the body. This is why, while it appears that indolent forms of breast cancer can safely be left untreated for years in some cases, once surgery is performed, it is important to follow up with additional appropriate treatment (such as radiotherapy, chemotherapy, and/or endocrine treatment) within a few weeks.

Morphine appears to amplify the deleterious effects of surgery. On the other hand, use of powerful nonsteroidal anti-inflammatory drugs (NSAIDs) during surgery could reduce the risk of recurrence, according preliminary studies. Some researchers have asserted that there is enough evidence concerning morphine to warrant taking steps to avoid its use. Many lumpectomies could probably be performed under regional anesthetic without morphine.

Latest research finds morphine promotes growth of existing tumors

The study referenced at the beginning of this news story was designed to investigate how morphine influences tumor initiation and development in an animal model of breast cancer. To conduct the study, the authors used transgenic mice with a tendency to develop mammary tumors similar to human invasive ductal breast cancer. Groups of mice were treated at different ages with clinically relevant doses of morphine or a saline solution (control).

Morphine was found not to influence tumor development when given before any tumors had appeared. In other words, mice given morphine early did not develop tumors sooner or in larger numbers than control mice who received no morphine. However, when morphine was given after tumors had started to appear in the mice, it significantly promoted tumor progression and reduced mouse survival times. Morphine treatment was shown to result in increased angiogenesis and elevate other markers of tumor progression. The authors conclude that morphine does not influence the onset of tumor development but promotes growth of existing tumors and reduces survival in mice.