Nevertheless, it would seem appropriate only to
perform a direct intratumoral injection if there
are clear and overriding advantages – and there
is scant evidence in the literature for such
advan-
tages.
It is also now clear from the literature that as
the sophistication of the methods used to gather
pathological evidence from sentinel nodes in-
creases, so there is improved sensitivity of
detec-
tion of micrometastases. What is not known is the
extent to which an ever – increasing sensitivity
leads to the detection of a few or even single
micro-
metastases in a lymph node which will fail to
develop clinical expression. This issue is raised
by
an editorial in the
Lancet
[2], where it is almost
claimed that all the power of modern histopatho-
logical evidence gathering should be aimed not
merely at the sentinel node but rather at all the
nodes cleared during a surgical axillary lymph
node clearance. That this is and probably will
remain an entirely impractical proposition is also
beyond doubt.
From a legal point of view, radiation protec-
tion legislation differs significantly from
country
to country but in general, a radiopharmaceutical
needs to be licensed before it is made available
for routine use. The tracers used in Europe for
lymphoscintigraphy and sentinel node detection
were mostly developed in the early 1970s and were
aimed at the imaging of the reticuloendothelial
system of the liver, spleen and bone marrow.
The properties and overall characteristics of
these tracers have therefore not been optimised,
in general, for sentinel node detection. There
is
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attempted to combine detection of the sentinel
node with detection of all lymph nodes in the
appropriate lymph basin (lymphoscintigraphy).
Furthermore there is significant controversy as
to
the minimum amount of histopathological evi-
dence which needs to be obtained from the sen-
tinel node.
It
is astonishing that groups have used such
varying techniques in terms of the delivery of an
appropriate radiopharmaceutical to the area of
interest (Figs.1–3). It is well known from the
lite-
rature that lymphatic tissue is most prevalent in
the peripheral layer of the skin, such that a sub-
dermal injection will deliver the tracer to an
area
rich in lymph vessels. It is also well known that
subcutaneous tissue has fewer lymphatic vessels
and that direct injection of the tracer into a
tumour will consequently entail the administra-
tion of an indicator into a high-pressure system.
By
their nature, tumours have high interstitial and
high intercellular pressures, and it is therefore
possible that any attempt to administer a tracer
directly into a tumour will only lead to leakage
of
the tracer from the tumour into the peritumoral
tissue. There is debate as to the safety of
punctur-
ing a tumour directly since there is concern that
this may lead to increased seeding of micrometas-
tases from the needle track and puncture of the
tumour. There is currently little evidence that
this
has any effect on the long-term evolution of the
chapter
1
2
3
2
1
Figs. 1– 3.
Possible routes for administration of tracer for
sen-
tinel node detection. The lymphatic-rich area is seen in Fig.
1
