Study: No Clinical Connection between Opioid Use and Breast Cancer Recurrence

Some of the challenges that come with treating pain patients with opioids are well-understood, including the potential for misuse and abuse, overdose and addiction, and adverse events including nausea, opioid-induced constipation, and confusion, among many others. Because of these negatives, pain practitioners were long wary of prescribing opioids. Thus, there aren’t many studies showing some of the potential impacts of the medications over time and with other co-morbidities, although this is area of research is expanding rapidly.

Opioids are often prescribed for breast cancer patients, who may experience mild to severe pain, acute or chronic, both because of the cancer itself (most common if the cancer has spread to other parts of the body, such as the bones, or as a result of treatments, including surgery, chemotherapy, or radiation therapy. But is there a chance that opioids could in some way contribute to the potential recurrence of cancer for those patients?

A recent Danish cohort study, published in Cancer, looked at the potential association between post-diagnosis opioid use and breast cancer recurrence and found some good news: there is no clinically relevant evidence of an association between opioid prescriptions and breast cancer recurrence.

The study makes good use of the DBCG (Danish Breast Cancer Cooperative Group) Registry formed in 1975 as part of an effort to establish a nationwide standardization of breast cancer treatment and collect relevant clinical data in a national database. Patients with incident, early-stage breast cancer who were diagnosed between 1996 and 2008 were identified and cross-matched with opioid prescriptions taken from the Danish National Prescription Registry. Follow-up began on the date of primary surgery for breast cancer and continued until breast cancer recurrence, death, emigration, 10 years, or July 31, 2013, whichever occurred first.

The study authors then used Cox regression models to compute hazard ratios and 95% confidence intervals associating breast cancer recurrence with opioid prescription use overall and by opioid type and strength, immunosuppressive effect, chronic use (≥6 months of continuous exposure), and cumulative morphine—equivalent dose. The final tally was 34,188 patients who met the study criteria. Analysis of this group showed that there was no association between patients who had used opioids and breast cancer recurrence—regardless of opioid type, strength, or cumulative dose.

The study authors note, “Breast cancer recurrence rates were lower among users of strongly (but not weakly) immunosuppressive opioids, possibly because of channeling bias among those with a high competing risk, because mortality was higher among users of this drug type.”