Around 75% of the 48,000 women annually diagnosed with breast cancer in the UK suffer from an estrogen receptor positive tumor, which implies the involvement of the hormone estrogen in cancer growth. Tamoxifen and exemestane are both hormone treatments, and whilst tamoxifen blocks the tumor’s ability to use estrogen, aromatase inhibitors, such as exemestane reduce the body’s production of estrogen.

Findings in The Lancet Oncology now reveal that a drug therapy that reduces the risk of women dying from breast cancer exposes these women to a higher risk of developing carpal tunnel syndrome, however, this can be managed and does not persist once treatment has finished.

Women with early stage estrogen receptor-positive (ER+ or hormone sensitive) breast cancer often receive drugs for five years following surgery to help prevent recurrence of the disease.

A multi-national 37-country Intergroup Exemestane Study (IES) of over 4,700 women previously reported that women who switched to exemestane after two to three years of tamoxifen tended to have a lower recurrence or mortality rate as compared with women remaining on tamoxifen for the entire five year period.

However, the IES also showed that more women (42.4%) in the exemestane group reported musculoskeletal symptoms, such as bone fractures, joint or muscle pain during treatment and particularly carpal tunnel syndrome (2.8%) compared with those in the tamoxifen group (33.2%), of which only 0.3% developed carpal tunnel syndrome.

These musculoskeletal side effects have been reported in more detail by the Institute of Cancer Research and Imperial College London in the UK, and the Leiden University Medical Center in the Netherlands.

Carpal tunnel syndrome is pressure on the median nerve in the wrist, which leads to numbness, muscle weakness or pain in the fingers and hand. The study participants who developed carpal tunnel syndrome suffered on average for six months, and whilst most received successful surgery for this side effect, very few patients discontinued their treatment because of carpal tunnel syndrome.

The researchers noted that the occurrence of carpal tunnel syndrome in those who completed treatment was very low. The researchers observed no difference in the occurrence rate of carpal tunnel syndrome between the two groups.

Director of the Clinical Trials and Statistics Unit at The Institute of Cancer Research (ICR-CTSU), Professor Judith Bliss, states:

“The rate of carpal tunnel syndrome was higher in women who switched to exemestane than in those treated only with tamoxifen. We found more than half of patients who developed this side-effect had surgery, but the vast majority were able to continue their treatment for breast cancer and did not experience carpal tunnel syndrome once their treatment had concluded.”

Martin Ledwick, Cancer Research UK’s head information nurse, commented:

“This gives clinicians more information with which to help patients make fully informed treatment decisions. It is worth noting that carpal tunnel syndrome is usually treated successfully and this needs to be considered when balancing severity of side effects against benefits of different treatment options.”

Written by Petra Rattue