A Two-Phase Study Model for the Standardization of HER2 Immunohistochemical Assay on Invasive Ductal Carcinoma of the Breast
Pichet Sampatanukul MD, MSc*, Benjaporn Chaiwun MD**, Sansanee Wongwaisayawan MD***, Parvinee Suwanagool MD****, Songkhun Vinyuvat MD*****, Anant Karalak MD******, Niphon Praditphol MD*******, Paisit Paueksakon MD********, Preecha Ruangvejvorachai BSc*, Andrew S Field FRCPA, FIAC, DipCyt (RCPA)*********, Pongsak Wannakrairot MD*
Affiliation : * Department of Pathology, Faculty of Medicine, Chulalongkorn University ** Department of Pathology, Faculty of Medicine, Chiang Mai University *** Department of Pathology, Faculty of Medicine, Ramathibodi Hospital, Mahidol University **** Department of Pathology, Faculty of Medicine, Siriraj Hospital, Mahidol University ***** Institute of Pathology, Department of Medical Service, Ministry of Public Health ****** Pathology Division, National Cancer Institute ******* Pathology Division, Rajavithi Hospital ******** Department of Pathology, Phramongkutklao College of Medicine ********* St Vincent’s Hospital, Sydney, Australia
Objectives : To develop and verify a standardized protocol for HER2 immunohistochemical assays on invasive
ductal carcinoma of the breast in Thailand.
Materials and Methods : A two-phase study approach was employed. In the Phase One, after verifying the
proposed protocol that adopted the HercepTest procedure using readily available primary antibodies, CB11
and A0485, Lab 1 performed the HER2 immunohistochemical staining for 137 cases of invasive ductal carci-
noma twice with two types of the antibody. Nine pathologists from 8 centers independently examined and
scored all the 2x137 stained slides that were blinded for antibody type. Interobserver reliability was calcu-
lated using pair-wise kappa. Following discussion of the results, the Phase Two study was planned. Lab 2 and
Lab 3 independently performed the HER2 staining according to the protocol for 60 invasive breast carcinoma
cases. The same group of pathologists scored 2x60 stained slides that were masked for laboratories. Interobserver
reliability and interlaboratory agreement from each pathologist were calculated using kappa statistics.
Three interpreted categories - namely negative, equivocal and positive tests were used in the analyses.
Results : Phase One study showed interobserver agreement between pairs varied from kappa 0.75 (95%CI,
0.68-0.82) to 0.06 (95%CI, 0-0.14) while Phase Two study obtained pair-wise kappa scores ranged from 0.84
(95%CI, 0.80-0.89) to 0.65 (95%CI, 0.59-0.71). Interlaboratory kappa for each pathologist was 0.67 (95%CI,
0.61-0.73).
Conclusion : The standardization of HER2 immunohistochemical assay was achieved through this two-phase
study model. It had added benefits of improving pathologists’ expertise and verifying the HER2 testing proto-
col to be used in Thailand.
Keywords : HER2, IHC, Immunohistochemistry, Breast carcinoma, Guideline, Standardization
