Does doxycycline improve breast cancer treatment?

Breast cancer is the most common cancer in women, causing a significant number of cancer cases and deaths. Despite successful treatment, the disease comes back in about one of five patients. 
It has been shown that cancer starts from special cells called “cancer stem cells”. These stem cells make up 5 to 10% of the tumor cells but are hard to kill with standard anticancer treatments like chemotherapy or radiotherapy, and therefore responsible for cancer spread and return of the disease. 
Multiple studies recently reported that doxycycline, a well-known and widely used antibiotic which can be taken as a tablet, can effectively target cancer stem cells. A small study conducted with breast cancer patients showed that when doxycycline was added to the regular treatment the amount of cancer stem cells was reduced by 40% after just two weeks. 

Aim
Our goal is to find out (a) if the standard anticancer treatment for early hormone sensitive breast cancer can be improved by adding doxycycline to the regular treatment and (b) if doxycycline is well tolerated when given along with chemotherapy. 

Methods and approach
We will ask 50 patients with early hormone-dependent breast cancer to take doxycycline by tablet along with their standard chemotherapy before they undergo surgery. We will analyze tissue samples to see how the treatment worked and whether there is any change in the number of cancer stem cells before and after treatment. Patients will participate in this study from the start of medical treatment until surgery, which will take place after 6 months. Patients will have to visit their doctors several times during treatment as also done for patients being treated outside of the study. Two additional visits are necessary for participants in the study. Tissue samples will be taken before surgery and during surgery, with no additional interventions.

Benefit for future patients
Patients with breast cancer that is hormone sensitive represent 35 to 40% of patients’ requiring chemotherapy before surgery. In this group, only about 15% of the patients see their cancer disappear completely after their treatment. Adding a drug which specifically targets cancer stem cells is likely to improve the treatment for these hormone-dependent tumors, thus increasing the survival of patients. In addition, the results of this trial will help to design future clinical trials with interventions acting against cancer stem cells.