When is localized prostate cancer clinically insignificant?

Among prostate cancer specialists, there has been a broad acceptance — for some time — of the idea that a localized prostate cancer “index” tumor with a Gleason score of 6 or less and a volume of ≤ 0.5 cm3 could be considered to be clinically insignificant and therefore did not (necessarily) need to be treated. Obviously, however, if such a tumor continued to grow over time, it might reach a point at which treatment became necessary.

A new analysis of data from the European Randomized Screening Study for Prostate Cancer (ERSPC) has now suggested that significantly larger “index” tumors might also meet criteria for clinically insignificant disease. This suggestion — which clearly needs to be validated — may have many implications. (Note that the “index” lesion or tumor is defined as the tumor with the largest identifiable volume.)

According to the new study by Wolters et al., scheduled for publication in the January issue of the Journal of Urology, the researchers were able to calulate the rate of insignificant prostate cancer based on estimates of lifetime risk of prostate cancer in screened and non-screened participants in the ERSPC.

Their calulations suggest that 50.8 percent of screen-detected prostate cancers are clinically insignificant. This allowed them to use data from the 49.2 percent of 325 radical prostatectomy specimens with the largest tumor volumes to estimate a threshold tumor volume for clinically significant prostate cancer.

The basic results of their analysis are as follows:

  • The maximum index tumor volume for clinically insignificant disease is 0.55 cm3.
  • The maximum total tumor volume for clinically insignificant disease is 0.70 cm3.

However, after making adjustments to the model to allow for tumor stage and tumor grade, the researchers were able to estimate that, for men with a Gleason score of 6 or less and a cancer with a pathologic stage of pT2 (i.e., truly localized disease):

  • The maximum index tumor volume for clinically insignificant disease is 1.3 cm3.
  • The maximum total tumor volume for clinically insignificant disease is 2.5 cm3.

If these results can be confirmed, they will necessitate a careful re-analysis of current methods used for pretreatment risk assessment, which will also have implications for eligibility for and use of active surveillance as a disease management option.

Combination of data from new studies on the clinical significance of tumor volume and the co-morbidities of newly diagnosed patients (as suggested by D’Amelio just the other day) would have major impact on the guidance that could be offered to newly diagnosed patients about management of their condition.

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