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PCR Assay Finds Occult Melanoma Metastases in Sentinel Nodes, Promises More Accurate Staging

PCR Assay Finds Occult Melanoma Metastases in Sentinel Nodes, Promises More Accurate Staging

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.

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