Lymph node status is the most important factor related to prognosis. If the lymph nodes do not contain cancer, the status is "negative". If they do contain cancer, the status is "positive". Cancer that is found only in the breast has the best prognosis. Prognosis is worse when cancer has spread to the lymph nodes (lymph node-positive). And, as the number of cancerous lymph nodes increases, survival decreases [5].
Lymph nodes are small clumps of immune cells that act as filters for the lymphatic system. The lymphatic system, like the circulatory (blood) system, runs throughout the body and carries fluid, cells and other material. The lymph nodes in the armpit (the axillary lymph nodes) are the first place breast cancer is likely to spread. Figure 4.4 shows the location of the axillary lymph nodes.
Assessing axillary nodes
About 40 percent of women diagnosed with breast cancer have cancer in their axillary lymph nodes [8]. Lymph node status can sometimes be determined during a physical exam. This method is quick and easy, but it does not take the place of a pathologist’s exam of the lymph nodes removed during a biopsy. During a physical exam, a health care provider feels under the arm to check if the lymph nodes are enlarged. If they are, it is likely that cancer has spread. However, if your provider does not feel enlarged nodes, this does not mean that the nodes are cancer-free. Nearly one-third of women with negative nodes based on a physical exam in fact have nodes with cancer when they are studied under a microscope [9]. And, some women with enlarged nodes during a physical exam in fact have cancer-free nodes [8]. Therefore, a physical exam of the axillary nodes is not a precise way to check lymph node status.
The best way to determine whether lymph nodes have cancer is to look at the nodes under a microscope after they have been removed. In the past, most lymph nodes were assessed using an axillary dissection. During this procedure, a surgeon removes some lymph nodes (at least 10) from different layers of tissue in the armpit. These nodes are then sent to a pathologist for testing. Using a microscope, the pathologist looks at the nodes to decide whether they contain cancer. If they do, the pathologist counts the number of positive nodes (those that have cancer) and uses this information to help determine prognosis.
Although axillary dissection is still used, it is now more common to have a less invasive procedure called sentinel node biopsy. Sentinel node biopsy removes only one to three lymph nodes. During this procedure, the surgeon injects a blue dye and/or radioactive-labeled liquid into the breast near the tumor. Then, using the dye and/or radioactivity as a guide, he/she finds the first node that filters lymph fluid from the tumor site (the sentinel node). Sometimes more than one node is labeled as a sentinel node. The sentinel node(s) is removed and examined by the pathologist for cancer cells. Only if cancer is found in the lymph nodes will an axillary dissection be done.
Some questions remain about the effect of sentinel node biopsy on rates of breast cancer recurrence and survival compared to axillary dissection. However, studies show that sentinel node biopsy is a good way to assess node status, especially when done by an experienced surgeon [8-15]. The results of a pooled analysis of 69 studies found sentinel lymph node biopsy correctly predicted lymph node status in 96 percent of women with breast cancer [11]. And, the false negative rate (or chance that the biopsy will show that cancer has not spread to the nodes when in fact, it has) is about seven percent [11].
There are many advantages of sentinel node biopsy over axillary dissection.
- It is accurate when done by surgeons experienced in the procedure.
- It is less invasive than axillary dissection.
- It has fewer side effects (such as lymphedema) than axillary dissection.
- It allows axillary dissections to be done only on those with cancerous sentinel nodes.
The disadvantage of sentinel node biopsy is that its accuracy depends on the experience of the surgeon [8]. Accuracy is still under study in certain groups, including people with features of locally advanced breast cancer and those who get chemotherapy before surgery (neoadjuvant chemotherapy) [8].
Updated 10/26/09
