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Interrogation of Sentinel Lymph Nodes Finds Hidden Metastatic Melanoma

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Identifying, removing and analyzing a few select lymph nodes often tells the tale

newer.jpgA 38-year-old woman comes to her dermatologist with a mole on her right upper back that has begun to itch and bleed. Examination shows that the mole has irregular borders and varied coloration. A biopsy reveals that it's a melanoma, 2.8 mm deep and with ulceration. There were no clinical signs or symptoms indicating that the melanoma had metastasized. A surgical oncologist recommends wide excision of the primary tumor site and a sentinel lymph node biopsy.

This case, paraphrased, opens an invited article in the May 5 issue of the New England Journal of Medicine by two MD Anderson surgeons. It provides a clinical update on a surgical lymph node biopsy technique that facilitates evaluation of possible microscopic spread of melanoma and indicates who needs further treatment.

MD Anderson was one of the first institutions to use sentinel lymph node biopsy, 20 years ago for melanoma and expanding into other cancer types.

"Sentinel lymph node biopsy allows us to obtain more information in the setting of less invasive surgery than our historical approach," says Jeffrey Gershenwald, M.D., co-author with Merrick Ross, M.D., both professors in the Department of Surgical Oncology. "And this allows a more personalized approach to surgery for our patients."

Lymph nodes are tiny round organs of the immune system that serve two important functions:

  • They are outposts for the foot soldiers of the immune system, such as T cells and B cells.
  • They trap cells and foreign particles that don't belong.
This second role usually makes lymph nodes that drain tumors the first place a cancer spreads.

Sentinel nodes are those regional lymph nodes that first receive lymphatic drainage from the tumor. To find them, surgeons inject patients with a radioactive tracer around the primary melanoma tumor site before surgeryas well as a blue dye. In complementary ways, tracer and dye help define the lymphatic pathway and show the two or three sentinel nodes in the regional nodal basin(s).

As part of the treatment approach for patients at sufficient risk for regional lymph node spread, both the tumor and sentinel nodes are removed in the same procedure.

An in-depth pathology analysis of the sentinel nodes identifies otherwise unobservable micrometastases. Gershenwald notes there are 10-35 lymph nodes in a given regional network draining any given tumor.

Before sentinel node biopsy was developed, the options for patients with early-stage melanoma at sufficient risk of having regional microscopic lymph node disease were to remove the primary tumor with a wide excision and

  • leave in place the lymph nodes to be followed by observation, or
  • have additional surgery to remove all nearby nodes (called elective lymph node dissection), even without clinical evidence of metastasis.
"The problem with these earlier options was that since only 15% to 20% of patients had metastasis to lymph nodes, 80% to 85% of patients had no potential benefits of aggressive lymph node surgery, yet were exposed to all of the potential associated risks," Gershenwald says.

NEJM_Video_image.jpgSentinel node biopsies and wide-excision surgical removal of the primary tumor are done during the same procedure. The sentinel node biopsy procedure generally is performed first to assure accurate identification of sentinel nodes, Gershenwald says.

Clinical guidelines of the American Joint Committee on Cancer (AJCC) and National Comprehensive Cancer Network call for patients with stage IB or stage II melanoma, as determined by tumor thickness, ulceration or rate of cell division (i.e., mitotic activity), to be offered sentinel node biopsy.

The patient in the case described above has stage IIB melanoma, so Gershenwald and Ross recommend surgical removal by wide excision and a sentinel node biopsy.

Today, patients with low-risk melanomas aren't generally offered a sentinel-node biopsy procedure as part of their initial management strategy.

"We are trying to define subsets of patients who have risk of micrometastasis even if, at first glance, their tumors suggest they are low risk," says Gershenwald, who co-chairs the AJCC committee on melanoma staging.

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