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The Sentinel Node in Colorectal Carcinoma

The Sentinel Node in Colorectal Carcinoma

The authors are to be complimented on a thoughtful and complete review of the
application of the sentinel node paradigm to colorectal cancer. This paradigm is
inherently quite different for colorectal cancer because, except for the
occasional demonstration of variant anatomy, the technique will not alter the
extent of surgery as it has done in melanoma and breast cancer.

Potential Clinical Utility

The authors review the many technical issues that remain unresolved in
applying the sentinel node concept to colorectal cancer including dye and/or
isotopes, in vivo vs ex vivo injections, subserosal vs submucosal injections,
colon vs extraperitoneal rectum, and the identification of nodes in the fatty
mesentery before the marker progresses to more central nodes. The latter issue
is the most problematic, with the sentinel and other close regional nodes buried
in the mesentery. For right colon cancers, nodes may be more easily identified
from the posterior retroperitoneal side after full mobilization.

Despite all these problems, the potential clinical utility of such studies
justify continued attempts to improve and standardize the technique. Although in
the future it is likely that analysis of molecular markers within the primary
tumor will provide the prognostic determinants for use of adjuvant regimens, the
presence of regional lymph node metastases is currently the primary indicator
for such treatments.

Micrometastases

The prognostic significance of colon cancer micrometastases is reviewed by
these authors, and the conclusion remains to be drawn. In a series of
standard node-negative stage II colon cancer patients whose regional nodes
were retrospectively examined for micrometastases by immunohistochemistry,
four-fifths of those alive without recurrence at 5 years had
immunohistochemistry-positive regional nodes.[1] If positive sentinel nodes
detected by immunohistochemistry or polymerase chain reaction (PCR) are
identified in otherwise node-negative patients, and are shown by prospective
studies to have an adverse prognostic impact, studies will still need to be
conducted to demonstrate the potential survival advantage of adjuvant therapy
and the risks associated with this incremental benefit.

A major challenge in defining the effect of micrometastatic-only nodal spread
on prognosis will be the ethical and logistical challenges to blinding such
findings from patients and treating physicians. Retrospective
immunohistochemical nodal analyses from a large multicenter cohort of routine
node-negative patients may be a more practical strategy for defining the
prognostic impact by multivariate analysis.

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