Lymph nodes are oval-shaped glands where immune reactions occur. For patients with endometrial cancer, lymph node status is an important factor for planning the cancer treatment course and predicting the status of the cancer. The "sentinel" node is the lymph node closest to the main tumor area, and it is believed to be at greatest risk for spread of the cancer. If the sentinel node does not contain cancer cells, then the remaining lymph nodes are usually cancer-free.