BUENOS AIRES--The techniques of lymphatic mapping, sentinel lymph node biopsy, and polymerase chain reaction (PCR) determination of occult metastases promise to provide a more accurate staging of the melanoma patient with more conservative surgery. This could save the health-care industry dollars and save patients the morbidity and expense of complete node dissection, Douglas Reintgen, MD, said at the Sixth World Congress on Cancers of the Skin.
In melanoma, routine histologic examination of the lymph nodes commonly misses micrometastatic disease. Although serial sectioning and immunohistochemical staining can double the rate of positive nodal dissections, these techniques have not been incorporated into standard pathologic practice because of the time and expense involved.
Lymphatic mapping and sentinel lymph node biopsy (see "Sentinel Node ID Allows Selective Lymphadenectomy"), however, allow full nodal staging from a detailed examination of only one or two nodes from the lymphatic basin. With this technique, use of serial sectioning and immunohistochemical staining becomes more practical. However, the rate-limiting step continues to be the number of sections of the node examined. Thus, an assay was needed for the accurate identification of all patients with occult or "submicroscopic" metastases.
Dr. Reintgen, associate professor of surgery, Moffitt Cancer Center and the University of South Florida, Tampa, said that initially his group tested cell culture techniques. Although accurate, these assays take up to 4 weeks to obtain results and are not widely applicable, since many community hospitals do not have tissue culture laboratories.
The Moffitt Cancer Center group then focused its research on development of an assay to analyze the sentinel lymph node preparation for the presence of tyrosinase messenger RNA (mRNA). The theory was that all cells of the body would have the gene for tyrosinase, but only those cells that are actively producing pigment would express the message for the gene.
A PCR assay was developed to analyze for the mRNA for the tyrosinase gene, with the hypothesis that mRNA found in the sentinel node is good evidence of the presence of metastatic melanoma cells, Dr. Reintgen said.
With PCR technology, one melanoma cell can be found in a background of 106 normal cells, orders of magnitude greater in sensitivity than routine histologic examination, a process that can identify one abnormal melanoma cell in a background of 104 normal lymphocytes.