EURURO Vol. 71 No. 5

765 844

11% of initial cases that could not be used because the
prostate cancer grade reported did not have both a primary
and secondary Gleason pattern recorded. The authors are to
be commended in trying to assess this weakness by
showing that even with 30% misclassification of grade
groups in both directions, the separation between the grade
groups remained. This statistical manipulation to help to
verify their data is only possible because of the several
hundred thousand cases within their study. Although the
SEER data are not as accurate as prior data from individual
institutions or limited multi-institutional collaborations for
analysis of grade groups, they have the benefit of reflecting
a more broadly based multiethnic population and general
pathology practice.
There are several advantages of the new five-tiered grade
grouping.
(1) Gleason score 7 is not homogeneous. Gleason score
4 + 3 = 7 has a much worse prognosis than Gleason score
3 + 4 = 7. Having distinct grade groups 2 and 3 for
Gleason scores 3 + 4 = 7 and 4 + 3 = 7, respectively,
clearly separates these grades to account for their
different prognoses and different treatment strategies,
particularly for patients treated with radiation therapy.
(2) Gleason scores 8–10 are often considered as one group
corresponding to high-grade disease. Grade group 4
(Gleason score 8) with its better prognosis is separated
from grade group 5 (Gleason scores 9–10) to better
stratify patients for different treatment strategies.
(3) The new grading system is simple andmore intuitive for
patients and physicians who are not prostate cancer
experts, with five grade groups as opposed to 25 scores,
depending on various Gleason pattern combinations.
(4) The lowest grade in the new system is 1, as opposed to
6 in the Gleason system; Gleason score 6 is the lowest
grade currently reported, although the scale goes from
2 to 10. Positioned in the middle of the Gleason scale,
Gleason score 6 is a deterrent to patient enrollment in
active surveillance. By contrast, grade group 1 out of
5 accurately denotes that this grade is the lowest
possible. This designation may help in changing patient
perception of the low malignant potential of this grade
and receptiveness to active surveillance, as recently
demonstrated in focus groups for prostate cancer
patients .
These new grade groups were formally accepted by the
World Health Organization in 2016. The new system has
also been accepted by the College of American Pathologists
(CAP), and the American Joint Committee on Cancer staging
manual (8th edition), which effectively means that they will
be included in virtually all pathology reports within the USA
once adherence to the guidelines is mandated at the
beginning of 2017. For the foreseeable future, grade
grouping will be reported alongside the Gleason score (ie,
Gleason score 3 + 4 = 7 [grade group 2]), and will eventually
possibly replace it in the future.
[3_TD$DIFF]1. Conflicts of interest: The author has nothing to disclose.
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