Researchers reviewed 16,975 cases of breast cancer diagnosed in Kaiser Permanente patients between 2000 and 2006. They found that for patients with the smallest HER2+ tumors (0.5 centimeters or less) who did not receive treatment with the antibody trastuzumab or chemotherapy, the chance of surviving five years without a distant recurrence (cancer that spreads outside the breast to other organs) was 99 percent. A distant recurrence is considered to be more threatening than a local recurrence in the breast.
For patients with the next size tumor (0.6 to 1 centimeter) the chance of surviving five years without a distant recurrence was 97 percent.
"Our results suggest that trastuzumab therapy may not be needed for patients with HER2+ tumors that are 0.5 centimeters in size or smaller, but should be considered for patients with larger tumors, with stronger consideration as the tumor size nears 1 centimeter," said lead author Lou Fehrenbacher, MD, medical director of Kaiser Permanente Oncology Clinical Trials and oncologist with Kaiser Permanente Vallejo Medical Center. "This is the first large study to demonstrate that the smallest lymph node-negative HER2+ breast cancers have a very low chance of returning."
Typical treatments for small, lymph-node-negative HER2+ tumors include surgery to remove the tumor and radiation therapy, although trastuzumab and chemotherapy are also frequently used to treat patients. HER2+ breast cancer, a subtype that accounts for between 15 and 20 percent of all cases of breast cancer in the United States, has been shown to respond well to trastuzumab. However trastuzumab can lead to heart failure in some women, particularly those who are older and who have other disease conditions.
Unlike larger tumors where distant recurrences are more common, the study found that the risk of local and distant recurrences was similar for these small HER2+ breast cancer tumors.