How reliable is Ki-67 immunohistochemistry in grade 2 breast carcinomas? A QA study of the Swiss Working Group of Breast- and Gynecopathologists.
Adjuvant chemotherapy decisions in breast cancer are increasingly based on the pathologist's assessment of tumor proliferation. The Swiss Working Group of Gyneco- and Breast Pathologists has surveyed inter- and intraobserver consistency of Ki-67-based proliferative fraction in breast carcinomas.


METHODS
Five pathologists evaluated MIB-1-labeling index (LI) in ten breast carcinomas (G1, G2, G3) by counting and eyeballing. In the same way, 15 pathologists all over Switzerland then assessed MIB-1-LI on three G2 carcinomas, in self-selected or pre-defined areas of the tumors, comparing centrally immunostained slides with slides immunostained in the different laboratoires. To study intra-observer variability, the same tumors were re-examined 4 months later.


RESULTS
The Kappa values for the first series of ten carcinomas of various degrees of differentiation showed good to very good agreement for MIB-1-LI (Kappa 0.56-0.72). However, we found very high inter-observer variabilities (Kappa 0.04-0.14) in the read-outs of the G2 carcinomas. It was not possible to explain the inconsistencies exclusively by any of the following factors: (i) pathologists' divergent definitions of what counts as a positive nucleus (ii) the mode of assessment (counting vs. eyeballing), (iii) immunostaining technique, and (iv) the selection of the tumor area in which to count. Despite intensive confrontation of all participating pathologists with the problem, inter-observer agreement did not improve when the same slides were re-examined 4 months later (Kappa 0.01-0.04) and intra-observer agreement was likewise poor (Kappa 0.00-0.35).


CONCLUSIONS
Assessment of mid-range Ki-67-LI suffers from high inter- and intra-observer variability. Oncologists should be aware of this caveat when using Ki-67-LI as a basis for treatment decisions in moderately differentiated breast carcinomas.
Institute of Surgical Pathology, University Hospital Zurich, Zurich, Switzerland.
Zsuzsanna
Z
Varga
Joachim
J
Diebold
Corina
C
Dommann-Scherrer
Harald
H
Frick
Daniela
D
Kaup
Aurelia
A
Noske
Ellen
E
Obermann
Christian
C
Ohlschlegel
Barbara
B
Padberg
Christiane
C
Rakozy
Sara
S
Sancho Oliver
Sylviane
S
Schobinger-Clement
Heide
H
Schreiber-Facklam
Gad
G
Singer
Coya
C
Tapia
Urs
U
Wagner
Mauro G
MG
Mastropasqua
Giuseppe
G
Viale
Hans-Anton
HA
Lehr
D001943:Breast Neoplasms / Q000175:diagnosis* / Q000188:drug therapy / Q000473:pathology; D017024:Chemotherapy, Adjuvant; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000378:metabolism*; D060787:Neoplasm Grading; D015588:Observer Variation
D019394:Ki-67 Antigen