Immunohistochemical Assessment of Hormone Receptor Status of Breast Carcinoma : Interobserver Variation of the Quick Score

Background: Immunohistochemical (IHC) assessment of estrogen receptor (ER) and progesterone receptor (PR) status has become a routine practice to predict the likely outcome of Tamoxifen therapy.
Aims: To assess the interobserver variation in scoring hormone receptor status of breast carcinoma, using the Quick Score.
Materials and Methods: IHC-stained slides of breast carcinomas reported by the two authors during a 28-month period were included in the study. Both authors independently reassessed all the tumors. Both were blinded to each other′s assessment. The Quick score with a 0-8 point scale was used to score the hormone receptor status. Weighted Kappa was calculated to assess the interobserver variation.
Results: A total of 210 breast carcinomas were included in this study. There was a substantial to almost perfect agreement between the two observers in scoring the hormone receptor status (kappa values; ER = 0.856, PR = 0.711). Both ER and PR showed an almost perfect agreement in assessing the intensity of staining (kappa value; ER = 0.882, PR = 0.840), while the scoring of proportion of cells gave lower Kappa values (kappa value; ER = 0.778, PR = 0.592). Interobserver agreement was less in scoring hormone receptor status of breast carcinomas after mastectomies compared with excision biopsies, wide local excisions and metastatic deposits in lymph nodes. Suboptimal fixation resulting in background staining has contributed to the variation.
Conclusion: A substantial to almost perfect interobserver agreement was seen in assigning an overall Quick score. Detection of complete negative and strong expression had a moderate to substantial agreement.