Fewer lymph node dissections and fewer positive lymph nodes: does it actually matter?

Surgical removal of samples of the pelvic lymph nodes at the time of radical prostatectomy (RP) — known as pelvic lymph node dissection (PLND)  — is still the most accurate method available to determine the presence or absence of lymph nodes positive for cancer (pN1 disease) in a patient with cancer of the prostate.

Abdollah et al. have assessed changes in the rate of application of PLND over the past 18 years, along with the number of lymph nodes actually removed and evaluated for the presence of cancer using frozen section pathology at the time of surgery (the lymph node count  or LNC). Their database comprised information available from 17 of the Surveillance Epidemiology and End Results (SEER) registries.

The results of this study are as follows:

  • 130,080 RPs were recorded in the 17 SEER registries between 1988 and 2006.
  • Patients were reported to have an unknown lymph node status (pNx) at the following rates
    • 25.9 percent across the entire 18-year timeframe
    • 20.8 percent between 1988 and 1993.
    • 30.1 percent between 1988 and 1993.
  • When PLND was performed, the average numbers of lymph nodes removed were
    • Mean 7.4 / median 6 across the entire 18-year timeframe
    • Mean 12.0 / median 12 in 1988
    • Mean 6.0 / median 4 in 2006.
  • Rates for positive lymph nodes (stage pN1) were
    • 3.4 percent across the 18-year timeframe
    • 10.7 percent in 1988
    • 3.1 percent in 2006
  • The LNC was an independent predictor of pN1 stage.

It is very clear that a decreasing proportion of prostate cancer patients have  lymph node staging carried out at RP today compared to 1988. The authors conclude that, as a consequence, fewer patients are being diagnosed with pN1 stage at RP. But this conclusion is not necessarily true.

There has been massive stage migration in the diagnosis of prostate cancer between 1988 and 2006, and it is not at all clear what effect such stage migration may have had on the real incidence of pN+ disease at surgery over time. Data published by Gallina et al. in 2008 can hardly be considered definitive since they are based on a small subset of the patients actually diagnosed in the USA and Europe during the period 1988 to 2005. Figure 1 from a paper by Cooperburg et al., also published in 2008, but based on data from > 10,000 patients in the CaPSURE database, clearly shows a 50 percent reduction in the incidence of high-risk prostate cancer in the USA between 1990-94 and 2004-07. But these authors report that, “There is no evidence for meaningful downward risk migration among high-risk patients over the past 15 years. At least some men in the high-risk group may be undertreated.”

At this point we don’t seem to know whether there has been a real reduction in the incidence of pN1 disease or just an apparent reduction as a consequence 0f fewer lymph node dissections. In a review earlier this year, Hyndman et al. conclude their abstract as follows: “There is good evidence that a pelvic lymph node dissection limited to the external iliac vein nodes is unnecessary in men with low-risk prostate cancer. A standard external iliac and obturator lymph node dissection, … makes sense in cases of intermediate and high risk. Harvesting a greater number of lymph nodes adds prognostic and even therapeutic benefit in many cases, including in some men with no obvious nodal metastases.” Perhaps what is needed is some stronger guidance on which patienst absolutely should and absolutely should lot receive a PNLD at the time of surgery, and how many lymph nodes should actually be sampled.

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