Breast cancer often spreads to other areas of the body through the 50 or so lymph nodes near a patient’s armpits, shoulders and upper arms.
These nodes are part of a network of glands that traverse our bodies, draining fluid wastes from our tissue. Once cancer enters this network from a diseased breast, it can metastasize—or spread—to other organs, causing new tumors.
Standard diagnosis for breast cancer has involved aspirating the tumor with a needle to extract cancer cells. Imaging techniques are also used to determine the tumor’s stage—that is, its size, shape and whether it has spread.
With this information, surgeons then perform either a lumpectomy, which removes the tumor only, or a mastectomy, in which the entire breast is removed. And these procedures often involve removing all the nearby lymph nodes through axillary lymph node dissection (ALND).
Now, doctors have found a new weapon that can detect a tumor’s progress and frequently spare a patient from unnecessary ALND. Called sentinel node biopsy, it assumes that cancer cells enter the lymphatic system through the two or three nodes that are the first to receive lymph fluid from the breast.
By identifying these so-called sentinel nodes, the disease’s progress often can be accurately determined. And if the nodes are disease free, it usually means the cancer hasn’t spread—and nearby lymph nodes don’t need to be removed.
That’s important, because ALND often complicates postoperative recovery and follow-up chemotherapy or radiation treatments. Trauma to the lymph system, known as lymphedema, frequently causes swelling, burning, pain and disability in the arms next to the tumor site because the lymph glands are clogged. This can make rehabilitation arduous.
What’s more, an estimated 70 percent of breast cancer patients with tumors classified as stage 1 or 2 (less than 20 millimeters in diameter) have no cancer in the lymph nodes—meaning many will undergo ALND needlessly. Furthermore, there’s no solid evidence that ALND improves the odds of long-term survival.
On the other hand, sentinel node biopsy is minimally invasive. The breast is numbed, then doctors inject a radioactive chemical or deep blue dye around the tumor. By watching the chemical or dye travel from the tumor to the lymph glands, doctors can spot the sentinel nodes and remove them for examination.
The sentinel node theory was first tested in the late 1970s for penile cancer and was adapted for breast cancer research in 1993. Even though it is still under development, many hospitals believe sentinel node biopsy could become a treatment of choice by the end of the decade.
To that end, research continues. In one completed study, sentinel node biopsy correctly identified disease-free lymph nodes 85 percent to 93 percent of the time. Two more large-scale studies are under way, sponsored by the National Cancer Institute. Both will assess the survival rates of women with stage 1 or 2 breast cancer who undergo sentinel node biopsy, conventional ALND or neither procedure.