Breast cancer drug “can stimulate tumour growth”

A drug prescribed to more than half of all patients suffering from breast cancer can in some cases actually stimulate tumour growth and increase the likelihood of a relapse, Swedish researchers said on Thursday.

The drug, tamoxifen, has since the 1970s been widely prescribed to fight breast cancer since it has shown to counteract the cancer-promoting effects of estrogen in the breast by binding itself to the estrogen receptor in the cancerous cell, thus impeding tumour growth.

According to new research conducted at the Malmö University Hospital, UMAS, in southern Sweden however, the drug can have the opposite effect on certain types of tumours.

“The result shows that tamoxifen is a very efficient treatment for most patients. But for 15 percent of tumours that contain many copies of the cell-splitting gene cyclin D1 tamoxifen however appears to have the opposite effect,” researcher Karin Jirström said in a statement.

The study conducted by Jirström and her colleagues was based on examinations of patients from southern Sweden who had been treated with the drug. It was recently published in the US medical journal Cancer Researcher.

“It is important not to draw the conclusion of this study too far … But this is the first time that patients have been identified on whom the treatment has had the opposite effect,” researcher Göran Landberg said in the statement.

“Our findings in Malmö should immediately be tested in other studies to avoid negative effects of this otherwise very effective drug tamoxifen,” he added.