Sentinal Node Biopsy Finds 98% of Metastic Colon Cancers

ORLANDO—Sentinel lymph node biopsy, which is widely used to detect micrometastases in melanoma and in breast cancer, can also identify colorectal cancer patients who have metastatic disease and should have adjuvant chemotherapy, Sukamal Saha, MD, reported in a plenary presentation at the Society of Surgical Oncology’s 52nd Annual Cancer Symposium (see Figure).

Dr. Saha, of Michigan State University, suggested that routine use of sentinel lymph node mapping in colorectal cancer patients might prevent false-negative lymph node examinations and improve survival prospects for the 55% of patients who do not have obvious nodal metastases but will nonetheless die of systemic disease within 5 years of diagnosis.

“If you look only at sentinel lymph nodes, the chance of missing microme-tastases is less than 0.4% in colorectal cancer,” Dr. Saha said.

This conclusion was based on a prospective study of 86 consecutive patients with colorectal cancer. In each patient, 1 mL of isosulphan blue dye was injected subserosally around the tumor. (Dr. Saha emphasized the importance of not injecting into the lumen.) The first one to three blue nodes identified within the first 5 minutes after injection of the dye were marked with sutures as sentinel lymph nodes.

An en bloc resection with regional lymphadenectomy was done, and 10 sections of each sentinel node were taken at 40-micron intervals at three levels. The entire specimen underwent standard pathologic evaluation. The sentinel node sections were stained with hematoxylin and eosin (H&E) for histologic examination and were also analyzed using immunohistochemistry for cytokeratin (Figure) and for carcinoembryonic antigen (CEA).

Study Findings

The study results were as follows:

At least one sentinel lymph node was identified in 85 of the 86 patients, the only failure being in a patient with low rectal cancer who had preoperative chemotherapy and radiation therapy. One or two sentinel lymph nodes were found in 90% of patients.

Sentinel lymph nodes were negative in 56 patients (66%); in 53 of these patients, all other nodes sampled were also negative. Thus, positive subsequent nodes (skip mets) were found in only 3 of the 56 patients with negative sentinel nodes.

Sentinel lymph nodes were positive in 29 patients (39%), and in 15 of these patients (18%), the positive sentinel node was the only sign of metastatic disease. In 7 of these 15 patients (9%), microme-tastases were found in only 1 or 2 sections of a single sentinel lymph node (see Figure). Identification of micrometastases in a sentinel node should have allowed these 15 patients to be upstaged to those most likely to benefit from adjuvant chemotherapy.

Dr. Saha said that sentinel lymph node mapping is successful in more than 98% of colorectal cancer patients and has a 96% accuracy for predicting the presence or absence of micrometastasis in the lymph nodes. The method used in this study is also cost-effective, since the dye costs only $31 per vial.

“This is a quick process. It requires only 5 to 10 minutes, needs no radioactive dyes, and allows the pathologist to focus attention on the one to three sentinel nodes,” Dr. Saha concluded.

The study was done in collaboration with investigators at Michigan State University; McLaren Regional Medical Center, Flint, Michigan; and Easton Hospital, Easton, Pennsylvania.

The researchers also presented their findings at the 35th annual meeting of the American Society of Clinical Oncology (ASCO), held in Atlanta, at an oral session on colorectal cancer (abstract number 905).