Abstract 3737: The effects of pregnancy on ERα and Her2/neu protein expression in the normal breast

Abstract

Abstract Introduction: Numerous epidemiological studies have established that a completed pregnancy is protective against breast cancer. However, the mechanisms through which pregnancy induces persistent changes in the breast, which translate into decreased cancer susceptibility, are poorly understood. One such change might be the reduction of ERα positive cells after pregnancy, supported by animal models and some evidence in the human breast. We recently reported that pregnancy causes a persistent downregulation of ERα expression at the mRNA level in the human breast that persists for up to 10 years; in addition, we reported a trend towards downregulation of Her2/neu (Asztalos et al. 2010). The purpose of the present study was to determine whether these mRNA findings were corroborated at the protein level by examining ERα and Her2/neu expression via immunohistochemistry (IHC) in the same set of human breast tissues. Patients and Methods: Women < = 45 years of age who had undergone reduction mammoplasty or a negative excision biopsy were eligible for the study, and were categorized as either nulliparous (NP), recently pregnant (within 2 years) (RP) or distantly pregnant (5-10 years since pregnancy) (DP). A tissue microarray (TMA) was constructed with triplicate 3.5 mm cores. The number of patients for each category was 12 NP, 11 RP and 12 DP. ERα clone 1D5 and Her2 polyclonal antibodies (Dako) were used and IHC was DAB based. TMA slides were scanned using an Aperio Scanscope-CS. ERα was quantified using a nuclear algorithm (identifies positive and negative nuclei) whereas Her2/neu was quantified using a positive pixel count algorithm as mostly cytoplasmic staining was observed. Statistical analysis was done in SAS using ANOVA to compare groups. Results: We found a statistically significant lower Her2/neu intensity in the recent pregnancy group compared to the other two groups (average intensity RP=127 vs DP=138 and NP=138, p < 0.02). There was no detectable difference in ERα expression patterns (per cent positivity or intensity) between the three groups. When the two parous groups were combined and analyzed against the nulliparous group, there was no significant difference between the two groups for either protein. Conclusions: This is one of few studies to investigate the influence of pregnancy on the expression of two important breast cancer biomarkers, ERα and Her2/neu, in benign breast tissue. The study differentiated between recent and distant pregnancy and thus was able to look for persistent changes that might occur. Although we did not find the same differences at the protein level that we saw at the mRNA level, this could be attributed to the lower sensitivity of the IHC technique compared to real time PCR coupled with the small number of samples that were used. Given the strength of epidemiological data, further studies are warranted. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3737. doi:10.1158/1538-7445.AM2011-3737