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Thursday, March 8, 2007

Lymph Node Dissection

[Updated May 4, 2009]

The natural course of prostate cancer is from the prostate to the seminal vesicles to the lymph nodes to the bone. If you are not familiar with the notion of lymph nodes read this short introduction first: [link].

Normally the first part of radical prostatectomy is to dissect some lymph nodes looking for cancer involvement.

At one time most surgeons aborted the surgery if such involvement were found but there is a trend today toward completing the surgery in any case.

The more lymph nodes are dissected the less the chance of missing cancer involvement whereas the fewer lymph nodes dissected the greater than chance of missing cancer involvement. On the other hand, if more lymph nodes are dissected there is a greater chance of complications.

There are several approaches to lymph node dissection (LND):

- Standard LND. The current standard method of LND is to limit the dissection to the obturator fossa. The argument in favor of standard LND is that in a Feb 2007 study of 4,693 patients, performing LND did not confer a statistically significant survival benefit relative to patients who had no LND at all. This was true overall as well as within risk strata.
[PMID: 17222625]

- Extended LND. An extended dissection also dissects lymph nodes outside the standard obturator fossa area and includes the hypogastric, external iliac and presacral regions. This provides for greater assurance that lymph node involvement is detected, if present, but carries the risk of greater complication and also increases surgery time. Another point in favor of extended LND is that not only is it more likely that lymph node involvement, if present, is detected but that it may be possible, in some cases, through meticulous dissection to remove all the cancerous tissue even if its migrated to the lymph nodes. In particular, the March 2003 paper [PMID: 12576797] points out that "in patients with positive nodes time to progression is significantly correlated with the number of diseased nodes. Some patients with minimal metastatic disease remain free of prostate specific antigen relapse for more than 10 years after prostatectomy without any adjuvant treatment. Meticulous pelvic lymph node dissection, particularly in patients with micrometastases, seems not only to be a staging procedure, but may also have a positive impact on disease progression".

- Sentinel LND. Among the lymph nodes the so-called sentinel lymph nodes (SLNs) are the primary landing sites for cancer involvement and if one can exclude the SLNs then one can exclude all lymph node involvement thereby dissecting fewer lymph nodes. SLNs can be detected using radioactive tracers administered 24 hours prior to surgery. These tend to accumulate in the sentinel lymph nodes and can be detected with gamma detectors. The paper referenced below claims there is little radiation risk from this procedure to either patient or staff as only 7.6 mSv is required. Sentinel LND is not affected by the size of the lesion and therefore detects even micrometastases effectively. [PMID: 17296375] [Full paper] discusses sentinel lymph node dissection. SLN LND is commonly practiced in breast cancer but despite its useful as a predictor of cancer specific survival [PMID: 18838212] does not appear to have found its way into standard practice in prostate cancer according to the blog of [Dr. Glode].

A March 2007 paper [PMID: 17296375] concludes that extended or sentinel LND should be done, rather than standard LND, since more than half of patients with lymph node involvement have such involvement outside the region sampled with the standard procedure.

The following is my comment. Given the observation of the aforementioned March 2007 report that standard LND has a high likelihood of missing cancer involvement in the lymph nodes it may not be suprising that no survival difference was found in the Feb 2007 report between LND and no LND. Had a more effective LND procedure been used, extended or sentinel, then some difference may have been observed. There may also be a problem in achieving statistical significance even in the presence of an effect since a relatively small number of patients have lymph node involvement.

Note that extensive lymph node dissection requires open surgery rather than laparascopic or robotic surgery according to this page by Dr. Slawin.

On that same page Slawin mentions that he performs more extensive lymph node dissections on patients with larger Gleason 7 tumors and on patients with Gleason 8 and above with any size tumor. Another approach might be to use nomograms such as found at to predict lymph node involvement and increase the aggressiveness of dissection the greater than probability of involvement.

An October 2008 review of Lymph Node Dissection is available in [PMID: 19044297] [Full Text]. A 2009 review of Lymph Node Dissection in European Urology is available in [PMID: 19297079] [Full Text}. Note the tables in particular in this last review.

Other Surgery Posts

RP vs. LRP vs. RLRP - Part 1. Open Surgery (RP)
RP vs. LRP vs. RLRP - Part 2. Laparascopic Surgery (LRP)
RP vs. LRP vs. RLRP - Part 3. Robotic Surgery (RLRP)
RP vs. LRP vs. RLRP - Part 4. What Surgeons and Others Say

Choosing a Surgeon - Part 1. Considerations
Choosing a Surgeon - Part 2. Finding a Surgeon

Inguinal Hernia and Prostatectomy

Seminal Vesicle Ablation

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