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Lymphoscintigraphy And Radio-Guided Surgery For Sentinel Lymph Node
Identification In Low-Risk Clinically Localized Prostate Cancer. (January
2006)
The venerable paradigm
that has serviced breast cancer management for years is the understanding
that the risk of systemic spread of breast cancer is proportional to the
number of involved lymph nodes. This tenet has been honed to the point
that metastatic disease in a single node warrants adjuvant therapy in
addition to treatment of the primary tumor. Sentinel node mapping in
breast cancer has been verified as a reliable method to identify the node
that most likely is metastatically involved. The status of that node
serves as a surrogate, accurate in >95% of instances, for any
cancer spread to lymph nodes. Two recent articles suggest that
prostate cancer management may be traveling the same pathway.
“Is There a Need for
Pelvic Lymph Node Dissection in Low-Risk Prostate Cancer Patients Prior to
Definitive therapy?” by Weckermann from Augsburg, Germany (European
Urology 47; 2005) states at the onset: “Approximately 60% of lymph nodes
would be missed limiting the field of resection to the obturator fossa
instead of performing a meticulous lymph node dissection along the
external iliac vein, obturator nerve, and internal iliac (hypogastic)
vessels”. Their study demonstrated that radio-guided (intraoperative)
pelvic lymph node dissection allowed the identification of one or more
“sentinel nodes (SLN)”. On the basis of this identification a biopsy
(possibly a laparoscopic biopsy), can be targeted to only the
radio-positive nodes, thereby avoiding the morbidity of a “full”
dissection, while at the same time detecting positive nodes that might
otherwise be missed.
Their study focused on
men with clinically localized, low-risk disease (PSA < 10 ng/mL; Gleason
score <6), of whom 8.5% (16 of 187) had positive prostate biopsies
from only in one lobe, and another 10.7% (9 of 84) who were
biopsy-positive in both lobes. “A median of 6 SLN and 5 NSLN were
dissected from each patient. All men with positive nodes had a single
positive SLN.” The location of positive nodes was: obturator fossa, 9;
external iliac, 5; internal iliac, 12; presacral, 1. Two patients were
positive in non-SLN. The Gleason score was upgraded in 24% of the RP
specimens.
In an accompanying
editorial Heidenreich, who has authored several articles on this subject,
referred to his own extended pelvic lymphadenectomy series in which no
positive nodes were found in 13 men with PSA levels of <10 ng/mL and
Gleason scores of 2-4. However, positive nodes were found in 10% (11 of
111) of men whose PSA levels were <10 ng/mL, but had Gleason scores of
5-7. His conclusion was that “The data further underline the inadequacy of
the currently used preoperative nomograms such as the Partin tables to
accurately predict pelvic lymph node disease.”
Weckermann points out
that the overall 6.8% of nodal positivity in his study is three times as
high as predicted in the updated Partin tables, which give an estimated
positivity of 0-2% for men with cT2b disease, PSA <10 and a biopsy
Gleason score < 6; and 0-3% for cT2c patients with the same PSA and
Gleason score. “With the standard lymph node dissection which is limited
to the obturator fossa and the external iliac nodes, 13 of 25 men would
have been left with positive lymph nodes in this low-risk group”, with the
consequence that the underdiagnosed men would likely not have been offered
the long term androgen suppression that was found beneficial in the
Messing study.
A second article,
“Limited pelvic lymphadenectomy using the sentinel lymph node procedure in
patients with localized prostate carcinoma”, European Journal of Nuclear
Medicine and Molecular Imaging, June 2005, investigated the location of
sentinel nodes using the radio-tracer technique. In 77% (21/27) cases a
SLN was identified along the initial centimeters of the hypogastric
(internal iliac) artery, a region not normally included in the standard
limited dissection; 40.7% (11/27) were located in the obturator fossa; and
18.5% (5/27) in the external iliac area. “Four patients had lymph nodes
metastases, all in SLN; two in the hypogastric area and two in the
obturator fossa”. No metastases were found in non-sentinel nodes.
A review by Wawroschek (Urol
Int 2003:709(4) of 350 cases studied with SLN technique found metastatic
deposits in 24.7% when the specimens were step sectioned. And in an
extension of the series (Eur Urol, Feb 2003), the number increased to
26.8% positive nodes in these men with clinically localized prostate
cancer. As his experience developed, he eliminated pathologic examination
of non-SLN. By sampling only nodes in the obturator fossa 44.2% of
positive nodes would have been missed, by adding sampling of the external
iliac region the sensitivity was increased to 65.4% of the total of
positive nodes found in the full dissection. Conclusion: “Limiting the
number of lymph nodes to the one with the highest probability of bearing
lymphatic spread (SLN) makes the use of extensive histopathological
techniques more feasible.”
Bottom Line:
The sentinel lymph node radio-guided biopsy technique offers the promise
of identifying the important minority of node-positive, low-risk patients
with clinically localized prostate cancer who might benefit from adjuvant
therapy.
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