Canadian scientists from the University of Toronto, together with doctors, studied the effect of double mastectomy (removal of cancerous breasts). The study was published in the scientific journal magazine JAMA Oncology.
The team examined data from 660,000 women, average age 58, diagnosed with unilateral breast cancer.
Once diagnosed, each patient underwent one of three standard surgical procedures: lumpectomy (removal of the tumor in the affected breast), unilateral mastectomy (removal of the entire breast), or bilateral mastectomy (removal of both breasts).
The researchers also followed the women for 20 years to see if they developed breast cancer in their remaining breast (a condition called contralateral breast cancer).
This can also happen to people who have had a double mastectomy because there is a chance that some of the remaining breast tissue or cancer cells may recur in the chest wall. The risk of contralateral breast cancer after a unilateral breast cancer diagnosis is usually about 0.4% per year.
Overall, women who had a double mastectomy had a significantly lower risk of developing contralateral breast cancer than the other groups (0.7% vs 6.9%).
However, there was no statistically significant difference in overall mortality rates between the groups; 16.3% for lumpectomy and 16.7% for both types of mastectomy.
Experts noted that one possible explanation for this contradictory finding could be that the primary cause of death in patients was the original tumor, not the contralateral breast cancer.
Earlier scientists in the name Treatment that provides protection against breast cancer recurrence for 10 years.