Concordance between Semi-Quantitative Immunohistochemical Evaluation and Oncotype Dx RT-PCR Derived ER, PR and HER-2 Status in Breast Cancer
R Jaffar, R Virk, D Kandil, S Lu, A Khan. UMassMemorial Medical Center, Worcester, MA
Background: Oncotype Dx is a commercially available 21-gene set expression profile by reverse transcriptase polymerase chain reaction (RT-PCR) in Stage I & II, estrogen receptor (ER) positive breast cancer (BC). In addition to reporting the recurrence score as high, intermediate and low risk, Oncotype Dx report also includes ER, Progesterone receptor (PR) and Her-2 neu scores derived by RT-PCR. In this study, we aimed to correlate Oncotype Dx RT-PCR based ER, PR and HER-2 with immunohistochemistry (IHC) derived ER, PR, and HER-2 scores.
Design: We reviewed the pathology reports on BC cases submitted for Oncotype Dx and recorded the ER and PR semi-quantitative immunohistochemistry (IHC) score using the SP1 and SP2 clones respectively. The HER-2 status, determined by IHC (A085 clone) and read by Chromavision automated cellular Imaging system (ACIS), was also retrieved. ER and PR data by both methods was available on 111 cases and HER-2 on 60 cases. Positive ER and PR staining on IHC was divided into 4 semi-quantitative grades, 1 (low positive), 2-10%, 2, 11-25%, 3, 26-75% and 4, >75% tumor cell nuclei immunoreactive. The HER-2 staining score by ACIS was divided in three groups, negative (0 to 1.5), indeterminate (1.5-2.9) and positive for HER-2 (≥3.0). All indeterminate cases on IHC were tested by Fluorescent in-situ hybridization (FISH) for HER-2 gene amplification. In Oncotype Dx, ER >6.5, PR>5.5 and HER-2>11.5 by RT-PCR is considered positive.
Results: ER grade by IHC was 1 in 5, 3 in 5 and 4 in 101 cases. In the PR positive group 22, 9, 21 and 59 were grade 1, 2, 3 and 4 respectively.For HER-2, 41/60 were negative by IHC and 19 were indeterminate (score 1.6 – 2.7), all the indeterminate cases were negative on FISH. There was 97% concordance between ER by IHC and RT-PCR; of the 3 cases negative for ER by RT-PCR, 2 had IHC grade of 1. PR status by RT-PCR showed less concordance with IHC; 23/111 (21%) cases converted from PR positive on IHC to PR negative by RT-PCR. Of these 23 cases PR grade by IHC was 1 in 15. Of the HER-2 negative, only 1/60 was called positive by RT-PCR. In this case FISH was also negative in the invasive component but it had a FISH amplified DCIS in close proximity to the invasive cancer.
Conclusions: Semi-quantitative ER and HER-2 grade by IHC correlates well with RT-PCR score but IHC may be a better test because of morphologic correlations. However, the threshold for PR positivity by IHC and RT-PCR needs to be re-evaluated especially the low PR positivity by IHC.
Tuesday, March 23, 2010 1:00 PM
Poster Session IV # 23, Tuesday Afternoon