A new study has reported that breast cancer surgery to remove the primary tumor may increase the metastatic potential of any remaining cancer. The study was designed to test the hypothesis that surgery induces changes in the expression of genes implicated in metastasis, thereby leading to accelerated metastatic tumor growth. Surgical removal of the primary tumor is a necessary and effective treatment for breast cancer patients. However, both animal and human studies have reported that surgery increases the growth of any residual tumor and micrometastases. In other words, tumor removal is followed by accelerated growth of locally recurrent tumors and metastases.

In the study, mouse mammary cancer cells were implanted in the mammary fat pads of 24 female mice. The mice were then equally divided into a surgery group in which the tumor was completely surgically removed after 21 days and a no surgery group. Metastatic tumor size and indexes of cancer cell adhesion, invasion, and angiogenesis were measured using various methods. The levels of 84 genes known to be involved in metastasis were also determined in both groups of mice.

Surgical removal of the primary tumor was found to be associated with increased number and size of metastases. Metastases in mice that underwent tumor removal demonstrated heightened proliferation, but no reduction in apoptosis (a type of cell death initiated to rid the body of defective and other unwanted cells). Surgery significantly increased the expression of genes involved in cancer cell adhesion, invasion, and angiogenesis.