Abstract P3-07-02: Prognostic and predictive relevance of HER2 status in ductal carcinoma in situ: Results from the UK/ANZ DCIS trial

Abstract

Abstract Background: As compared to invasive breast cancer (IBC), HER2 is much more frequently overexpressed in ductal carcinoma in situ (DCIS). Unlike IBC, the prognostic significance of HER2 overexpression remains to be established in DCIS and large studies to investigate its predictive role are lacking. We investigated the prognostic and predictive relevance of HER2 protein and ERBB2 mRNA expression in DCIS using material from UK/ANZ DCIS trial. Methods: Formalin-fixed paraffin embedded tissues (FFPETs) were collected from patients enrolled in the UK/ANZ DCIS trial, a randomised 2X2 factorial design trial investigating role of tamoxifen, radiotherapy or both as adjuvant treatment in DCIS. ERBB2 mRNA expression was evaluated by reverse transcription followed by PCR on customized Taqman low-density arrays. ERBB2 mRNA expression was analysed as a continuous variable and also as a binary variable using a cut-off to reproduce HER2 expression distribution similar to that observed with immunohistochemistry (IHC). HER2 protein expression was evaluated by IHC using HercepTest™ and scored as per ASCO-CAP 2013 recommendations; HER2 equivocal (IHC2+) were grouped with HER2 negative (IHC 0 or 1+) for main analyses. Additional analyses using binary ERBB2 mRNA expression as a reflex test for HER2 IHC2+ were also performed. Results: HER2 protein expression was evaluable in 713 (181 events) of 755 available samples (DCIS absent or lost during assay in 42). ERBB2 mRNA expression was evaluable in 521 (134 events) of 704 available samples (DCIS absent or insufficient RNA in 51, assay failure in 132). Both results were available in 508 cases (130 events). Increase in ERBB2 mRNA expression (median 0.62; range 0.07-36.76) was associated with increased risk of in situ ipsilateral breast event (DCIS-IBE) [Hazard ratio (HR) = 1.07; 95% Confidence Interval (95%CI) 1.04-1.10; p < 0.0001] but not with increased risk of invasive ipsilateral breast event (I-IBE) [HR = 1.03; 95%CI 0.97-1.10; p = 0.3209]. HER2 positivity by IHC was similarly associated with increased risk of DCIS-IBE [HR = 2.90; 95%CI 1.91-4.40; p < 0.0001] but not with increased risk of I-IBE [HR = 1.40; 95%CI 0. 0.81-2.42; p = 0.2313]. Reclassification of HER2 IHC2+ cases using binary ERBB2 mRNA expression (46 as negative, 16 as positive; 18 expression data unavailable) further improved prognostic discrimination of HER2 IHC [ΔX2 (1d.f.) 5.51; p = 0.0189] for any recurrence. The effect of radiotherapy (RT) for reducing I-IBE was greater in HER2 positive (by ERBB2 mRNA expression) cases [HR = 0.24; 95%CI 0.07-0.83; p = 0.0237] as compared with HER2 negative cases [HR = 0.60; 95%CI 0.23-1.55; p = 0.2925]. Kaplan-Meier estimates of 10-year I-IBE rates with and without RT were 4.5% (2.5%-1.4%) and 15.8% (9.6%-25.3%) in HER2 positive DCIS; rates in HER negative DCIS were 5.2% (2.1%-2.4%) and 7.3% (4.3%-12.2%) respectively. The differential benefit of RT by HER2 status was also seen for reduction in DCIS-IBE. Conclusions: HER2 overexpression is associated with increased risk of DCIS-IBE but not of I-IBE. HER2 status is predictive of radiotherapy response with larger reductions in both I-IBE and DCIS-IBE seen in HER2 positive DCIS. Citation Format: Thorat MA, Wagner S, Jones LJ, Levey PM, Bulka K, Hoff R, Sangale Z, Flake II DD, Bundred NJ, Fentiman IS, Forbes JF, Lanchbury JS, Cuzick J. Prognostic and predictive relevance of HER2 status in ductal carcinoma in situ: Results from the UK/ANZ DCIS trial. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-07-02.