The Multigene Assay Oncotype Dx Is Unnecessary for Low Grade Invasive Breast Carcinoma
JF Simpson, I Mayer, J Means, S Serie, ME Sanders. Vanderbilt University Medical Center, Nashville, TN
Background: The multigene assay Oncotype Dx uses RT-PCR to determine the expression of a panel of 21 genes in tumor tissue. The Recurrence Score (RS) is calculated from the gene expression results, ranging from 1-100. This assay is used to aid in the decision to administer adjuvant chemotherapy following a diagnosis of lymph node negative, estrogen receptor positive invasive breast carcinoma (IBC) and is the basis for selection for the TAILORx trial.
Design: Routine pathology parameters from all cases from our institution that have been submitted for Oncotype Dx testing were reviewed and correlated with the Recurrence Score (RS). Grade was assigned using the Elston and Ellis Combined Histologic Grade. Proliferation rate was determined by mitotic count/10 HPF, from the Combined Histologic Grade. Pearson's coefficient correlation (CC) was calculated for RS and Combined Histologic Grade, proliferation rate, and progesterone receptor status. RS was considered high for values greater than 31, intermediate for values 19-30, and low when less than 19. (NEJM 2004, 351:2817).
Results: Since June 2007, 23 cases have been sent for Oncotype Dx study. All were IBC of no special type . All patients were women, with an average age of 54 years. The average size of the IBC was 1.4 cm. The relationship between grade, proliferation rate and RS status is given in Table 1.
Correlation of RS with Histologic Features
|RS||inter/high grade||low grade||inter/high proliferation||low proliferation|
Histologic grade and proliferation rate correlated with RS (CC=0.50 and 0.56, respectively). This correlation was lost when low grade carcinomas (all of which had low RS) were excluded (CC=0.25). Similarly correlation with proliferation rate was reduced when cases with a low proliferation rate were excluded (CC=0.16). Progesterone receptor status was strongly correlated with RS (CC=0.84). Nineteen cases were PR positive, while 4 were PR negative; 3 of these were associated with a high RS and one had an intermediate RS.
Conclusions: Low grade carcinomas and carcinomas with a low proliferative rate are associated with a low Oncotype DX RS. Although the presence of PR does not predict an elevated RS, the absence of PR is associated with an intermediate or high RS. Oncotype DX should be reserved for intermediate or high grade invasive breast carcinomas.
Wednesday, March 11, 2009 1:00 PM
Poster Session VI # 21, Wednesday Afternoon