Radiation Therapy for Micrometastasis in Lymph Nodes
Dear OncoLink "Ask The Experts,"
Terry Styles, MD, Assistant Professor of Radiation Oncology at the University of Pennsylvania, responds:As in many areas of cancer care, local treatment of breast cancer continues to evolve. Two areas that are under evaluation is the use of radiation after mastectomy and the evaluation of the lymph node region.
For many years, the standard of care in patients receiving a mastectomy was to also have a complete axillary dissection at the same time. These lymph nodes were examined under a microscope for visible involvement with cancer cells. Patients with more than 4 positive lymph nodes were found to benefit from the addition of radiation in terms of local control and survival. Not quite ten years ago, 2 large studies were published demonstrating a benefit for patients with only 1- 3 positive lymph nodes. Because these studies were done on patients outside the United States with slightly different surgery than is done here, it is not yet the standard of care to recommend radiation after mastectomy if only 1 to 3 nodes are involved. A randomized trial is currently underway to evaluate whether the benefit seen in Europe would also be seen here in our patients. Nonetheless, individual assessment is essential to determine the benefit of post-mastectomy radiotherapy.
The second area undergoing change is the process used to evaluate the involvement of the lymph nodes. The advent of sentinel lymph node evaluation for breast cancer and melanoma revealed that careful evaluation of the sentinel lymph node with special stains demonstrated the occasional presence of small clusters of cancer cells in the lymph nodes. These clusters may contain just a few cells visible only with specialized staining (immunohistochemistry), or up to 2 mm with traditional staining (H&E). It became clear that these represented special cases of metastatic disease to the lymph nodes and as such, it is possible that standard prognostic information and treatment recommendations may not be as applicable.
Given the uncertainty of benefit of treatment for 1 positive lymph node and the uncertainty of whether a micrometatasis (either of a few cells on IHC or up to 2mm on H&E) is the same as our older definition of positive lymph nodes, it is hard for me to recommend post- mastectomy radiation in a patient with 1out of 8 lymph nodes showing micrometastases. Until additional studies are completed, there is little evidence at this time to support treatment based on this single micrometastatic lesion. Nodal involvement, however, is only one reason for post-mastectomy radiation, and decisions regarding the benefit of therapy are best made by a radiation oncologist who is fully knowledgeable of the details of your case.