Rare variants of adenocarcinoma of the prostate: a 25-year analysis of incidence and mortality


The vast majority of prostate cancers are adenocarcinomas of the prostate, i.e., cancers that start in the epithelial cells of the prostate gland. Most of these adenocarcinomas have a well-defined, “normal” cancer histology. However, there are five categories of rare adenocarcinoma, with differing levels of risk.

Marcus et al. have recently carried out a 25-year analysis of the available SEER data (from 1973 to 2008) in order to develop a thorough assessment of the incidence of these five rare forms of adenocarcinoma of the prostate and the associated mortality rates. The full text of this article has just been made available on the Medscape Oncology web site.

The five rare “variant” forms of adenocarcinoma of the prostate are:

  • Mucinous adenocarcinoma
    • Cases identified in the SEER database: n = 806
    • Incidence rate per million men per year: 0.61
    • 5-year overall survival rate: 75.1 percent
      • African Americans only: 64.8 percent
      • Caucasians only: 77.2 percent
    • Average (median) survival from diagnosis: 125 months
      • African Americans only: 99 months
      • Caucasians only: 144 months
  • Ductal (or intraductal) adenocarcinoma
    • Cases identified in the SEER database: n =662
    • Incidence rate per million men per year: 0.49
    • 5-year overall survival rate: 61.7 percent
      • African Americans only: 66.7 percent
      • Caucasians only: 60.2 percent
    • Average (median) survival from diagnosis: 84 months
      • African Americans only: 109 months
      • Caucasians only: 80 months
  • Signet ring cell adenocarcinoma
    • Cases identified in the SEER database: n =130
    • Incidence rate per million men per year: 0.08
    • 5-year overall survival rate: 60.5 percent
      • African Americans only: 76.0 percent
      • Caucasians only:  60.5 percent
    • Average (median) survival from diagnosis: 64 months
      • African Americans only: 100 months
      • Caucasians only: 64 months
  • Adenosquamous adenocarcinoma
    • Cases identified in the SEER database: n = 27
    • Incidence rate per million men per year: 0.03
    • 5-year overall survival rate: 22.4 percent
      • African Americans only:  50.0 percent
      • Caucasians only:  20.2 percent
    • Average (median) survival from diagnosis: 12 months
      • African Americans only: 20 months
      • Caucasians only:  11 months
  • Neuroendocrine (including small cell adenocarcinoma)
    • Cases identified in the SEER database: n = 502
    • Incidence rate per million men per year: 0.35
    • 5-year overall survival rate: 12.6 percent
      • African Americans only:  16.1 percent
      • Caucasians only:  12.8 percent
    • Average (median) survival from diagnosis: 10 months
      • African Americans only: 11 months
      • Caucasians only:  10 months

To put the level of rarity of these “variant” type of adenocarcinoma in context, have a look at the equivalent data for the standard (non-variant) type of adenocarcinoma seen in the vast majority of men:

  • Standard, non-variant adenocarcinoma
    • Cases identified in the SEER database: n = 790,937
    • Incidence rate per million men per year: 586.0
    • 5-year overall survival rate: 76.5 percent

And let us be very, very clear, immediately, that today’s 5-year overall survival rate for men diagnosed with standard, non-variant adenocarcinoma of the prostate is a great deal higher than 76.5 percent. The number given above encompasses the entire period from 1973 to 2008, but prior to about 1990 (i.e, for 17 of the 25 years) the vast majority of men would have been diagnosed only by the time that they had advanced or metastatic forms of adenocarcinoma of the prostate. Most men today are diagnosed with much earlier stages of their cancer.

This set of data is (as the authors note) the most comprehensive data set available to date on the incidence and mortality rates of rare subtypes of adenocarcinoma of the prostate. However, one should be very cautious indeed about over-interpreting the details of this data set. It does not give us good guidance on

  • Whether these patients were appropriately treated by comparison with today’s standards of care
  • Whether the variations in racial patterns are necessarily “real” (because the numbers of patients in the database are very small)
  • Whether many other men diagnosed with non-variant forms of adenocarcinoma may (in fact) have had a variant subtype that went undiagnosed.

The most important pieces of knowledge that we can probably extract from this data set at this time are the following:

  • Men diagnosed with mucinous adenocarcinomas seem to do about as well over time as men with non-variant adenocarcinomas.
  • Men diagnosed with adenosquamous and neuroendocrine adenocarcinomas are at very high risk for rapidly progressive disease and should probably be treated as aggressively as possible as quickly as possible.
  • There does appear to be a racial component to risk associated with at least some subtypes of adenocarcinoma.
  • The importance of accurate pathological diagnosis when there is any possible signal of risk for a non-variant subtype of adenocarcinoma of the prostate may be critical to the patient’s long-term outcome and survival.

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