Abstract P4-14-14: Clinicopathological features and endocrine therapy mode of ER low expression (1%-9%) breast cancer patients in China
Authors: Fu P , Wang S , Yao M , Xiang A , Li J , Wang H , Geng C , Jin F , Yin Y , Huang X , Jiang Z 
Published: May 2019

Abstract
Purpose: Since 2010, ASCO/CAP recommended that ER be considered positive if ≥1% tumor cells with positive nuclear staining by immunohistochemistry (IHC) in breast cancer. ASCO/CAP also recommended considering endocrine therapy (ET) in ER positive patients. However, most breast cancers are either ER negative or ER strongly positive (≥10%), and tumors with low ER (1-9%) expression are rare. Up to now, the effect of ET is controversial for these patients with ER 1-9% and unfortunately, we know little about the clinical information of this subgroup. In this study, we analyzed the clinicopathological characteristics and ET mode of patients with low ER expression. We sought to figure out whether the ASCO/CAP guidelines affect clinical ET decision in China and Which features are important considerations for doctors to choose ET. We also evaluated the efficacy of ET in these patients. Methods: Patients diagnosed stage I-III primary invasive breast cancer with ER low expression (1-9%) between January 2008 and December 2016 were retrospectively identified from six hospitals in China. Result: 457 patients (2.7%) had low expression of ER (1-9%) of 17216 patients. Mean age at diagnosis was 49 years. 288 patients (49.9%)were younger than 50 years old. 254 patients (55.6%) had stage II disease and 37 patients (8.1%) had lymphovascular invasion (LVI). 260 patients (56.9%) were HER2 positive; 408 patients had PR negative or low expression; 327 patients' (71.6%) Ki-67 status were &gt; 20%. 388 patients (85%) received chemotherapy. Of those 388 patients, 90% patients received anthracycline combined with taxol chemotherapy regimens. 170 patients (37.2%)received ET. Before 2010, only 25.7% patients with low ER expression received ET. The proportion of ET increased after the 2010 ASCO/CAP guideline was published. In 2013, 50% patients received ET. The rate of ET was totally different in six hospitals. 55% patients received ET in the hospital with highest rate, while only 4% patients received ET in the hospital with lowest rate. Using the univariate logistic regression analysis of ET, ER expression, PR expression, Ki-67 status and LVI were associated with the rate of ET. But after adjustment for other covariates, only ER level was significantly associated with the rate of ET. Compared to patients with ER&lt;5% tumors, patients with ER≥5% tumors had a significantly higher probability of ET rate (OR, 2.882; 95% CI: 1.928-4.308; P &lt; 0.001). Median follow time was 30 months. The 5-year RFS rate was 85%. Younger age and positive lymph nodes were associated with worse RFS. Survival rate did not differ significantly between patients with or without ET (without ER vs with ET: OR, 0.870; 95% CI: 0.508-1.448; p=0.61). Conclusions: 2010 ACSO/CAP recommendation indeed result in an increase of ET rate for patients with 1%-9% ER positive. But these patients do not appear to benefit from ET. Prospective studies are needed for these patients and we need more accurate way to evaluate ER levels, which associate with endocrine response.
Citation Format: Fu P, Wang S, Yao M, Xiang A, Li J, Wang H, Geng C, Jin F, Yin Y, Huang X, Jiang Z. Clinicopathological features and endocrine therapy mode of ER low expression (1%-9%) breast cancer patients in China [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P4-14-14.