96. Jahrestagung der Deutschen Gesellschaft für Pathologie e. V ...

SO-027
Ki-67 in mitotic score groups of the Nottingham Grading System
for breast cancer
C . Focke 1 , D . Gläser 1 , K . Finsterbusch 1 , T . Decker 1
1 Dietrich-Bonhoeffer-Klinikum Neubrandenburg, Department of Pathology,
Neubrandenburg
Aims. The 2011 St. Gallen Consensus suggested the addition of Ki-67 for
defining proliferation and thus the difference between luminal A and
B clinicopathological subtypes. Whereas a Ki-67 cut-off of 14% is cited
from literature it became obvious from the discussion that no standardized
methodology or cut-off definition for Ki-67 is available so far. To
estimate the capability of immunohistochemically quantified Ki-67 rates
to discriminate the Nottingham Grading System (NGS) mitotic score
groups and to determine respective cut-offs in breast cancer (BC).
Methods. We retrospectively analyzed routinely H&E stained slides of 50
invasive BC (9 G1, 23 G2, and 18 G3). Immunohistochemistry for Ki-67
was done prospectively according to an in house protocol, evaluated in a
national interlaboratory trial for quality assurance in immunohistochemistry.
To rate Ki-67, 100 tumor cells within an area of the “hot spot “
were evaluated by counting all stained nuclei regardless of intensity. We
used the mitotic activity index (MAI) per mm2 as gold standard for proliferation
measurement. By assessing the MAI ranges within the mitotic
score subgroups of the Nottingham Grading System (NGS) we determined
respective MAI cut-offs. Using these MAI cut-offs we adjusted the
observed Ki-67 rates.
Results. Whereas the cut-offs of MAI for NGS mitotic scores 1, 2, and 3
were 0–32, 33–70, and 71–582, respectively, the resulting ranges of Ki-67
were 7–30%, 13–54%, and 33–98%. The median Ki-67 rates for NGS scores
1–3 came out with 21 (SD±7.5), 41 (SD±11), and 59 (±18.8), respectively.
Conclusions. Whereas there is obviously a trend of higher Ki-67 rates in
NGS score groups with higher MAI, our data indicate that 1) it was not
possible to discriminate the NGS mitotic score groups by using Ki-67
rates, 2) the cited cut-off of