Sentinel Node ID Allows Selective Lymphadenectomy

BUENOS AIRES--The surgical care of the melanoma patient is influx because of new data showing that complete nodal staging canbe obtained with the technique of lymphatic mapping and sentinellymph node biopsy, said speakers at a plenary session at the SixthWorld Congress on Cancers of the Skin.

Douglas Reintgen, MD, of the Moffitt Cancer Center, Tampa, Fla,explained that the concept is based on the belief that lymphaticdrainage is not a random event, but that the precise node thatdrains an area of skin can be identified.

The sentinel lymph node is defined as the first node in the lymphaticbasin into which the primary melanoma drains, and reports fromfour centers (John Wayne Cancer Institute, Moffitt Cancer Center,M.D. Anderson Cancer Center, and the Sydney Melanoma Unit) haveshown that the histology of the sentinel lymph node reflects thehistology of the remainder of the nodal basin.

With the lymphatic mapping technique, only patients with solidevidence of nodal metastatic disease, those with a positive sentinellymph node, are subjected to the expense and morbidity of a completenode dissection.

This strategy of selective lymphadenec-tomy would seem to satisfyboth the proponents and critics of the previous nodal stagingprocedure--elective lymph node dissection. All patients wouldundergo complete pathologic staging of their lymphatic basins,and most would be spared a complete lymph node dissection.

The first step with this technique involves lymphatic mappingvia preop-erative lymphoscintigraphy--the injection of a radiocolloidaround the primary melanoma site--with imaging of the afferentlymphatics and the regional nodal basin (see figure).

Intraoperative lymphatic mapping to harvest the sentinel lymphnode for biopsy is then performed using either a vital blue dyeor a radiocolloid.

William McCarthy, MD, of the Sydney Melanoma Unit, said that athis institution, preoperative lymphoscintigraphy has been usedto:

1. Define all lymphatic basins at risk for metastatic disease.

2. Identify "intransit" areas of lymphatic flow ("intransit"nodes are defined as nodal collections located somewhere betweenthe primary site and the regional basin, and are found in approximately5% to 10% of all melanomas).

3. Localize the sentinel node in relation to the remainder ofthe nodes in the lymphatic basin.

4. Estimate the number of sentinel nodes to be harvested.

Use of lymphoscintigraphy has demonstrated some unusual lymphaticdrainage patterns, and several new pathways have been identified,Dr. McCarthy said.

These include 26% of melanomas on the back showing drainage toan "intran-sit" node near the scapula in the intramuscularspace; 20% of melanomas near the umbilicus revealing drainageto an internal mammary node; posterior scalp melanomas drainingto lymph nodes at the base of the neck; and, in at least one patient,a forearm melanoma showing direct drainage to the ipsilateralneck.

With these data, Dr. McCarthy called into question the validityof previous studies of elective lymph node dissection, statingthat unless preoperative lymphoscintigraphy is performed, electivedissection may be misdirected in up to 50% of cases of trunk melanoma.

Learning Curve

Using preoperative lymphoscintig-raphy as a guide, surgeons atDr. McCarthy's institution had an initial 87% success rate inidentifying the sentinel lymph node. There was a learning curve,in that the success rate in the last 100 patients was 97%.

Cutaneous lymphoscintigraphy has been performed in 800 patientswith melanoma at the Sydney unit and used as a guide for subsequentsentinel node harvesting. Of these patients, 23% were found tohave micrometastatic disease in the sentinel node and were thentaken back to the operating room for a complete node dissection.

Initially, after harvesting, frozen sections of the sentinel nodewere examined for micrometastatic melanoma, but a false-negativerate of 9% caused the clinicians to abandon this practice in favorof permanent section examination of the sentinel node with multiplesections and immunohistochemistry staining. [See "PCR AssayFinds Occult Melanoma Metastases in Sentinel Nodes, Promises MoreAccurate Staging".]

Dr. McCarthy reported a 1.9% false-negative sentinel node ratewith the mapping technique at the Sydney unit. This figure refersto the occurrence of a regional nodal recurrence after a negativesentinel node biopsy and reflects the experience at other institutions.