Abstract GS2-05: Genome-wide Association Study Identifies UACA As a Modulator of Breast Cancer Chemoresistance and Survival

Abstract Prior studies suggest a strong genetic influence on breast cancer prognosis. Six genome-wide association studies (GWAS) on breast cancer prognosis have been published to date. However, none of the reported loci was replicated across studies and only two passed genome-wide significance (P < 5 x 10-8). In the Pathways Study, a prospective cohort of breast cancer survivors begun in Kaiser Permanente Northern California (KPNC) in 2006, we carried out a GWAS of overall survival (OS) in 3,973 patients. Trans-ethnic meta-GWAS identified an association with OS of a locus on chromosome 15 that almost reached genome-wide significance (P = 9.42 x 10-8). This locus spanned the UACA gene, a key regulator of tumor suppressor Par-4. We found that receipt of chemotherapy modified the effect of the UACA locus on OS (Pinteraction = 2.4 x 10-4). This observation led us to hypothesize that the UACA locus effect on OS may be specific to Par-4 dependent chemotherapies, which include anti-HER2 therapy and doxorubicin. We stratified patients into two groups, those who received Par-4 dependent chemotherapy agents versus other patients. In separate trans-ethnic meta-GWAS, the UACA locus was significantly associated with OS in patients taking Par-4 dependent chemotherapies (P = 1.27 x 10-9), while no association was observed in the other patients (P = 0.21). To evaluate whether the UACA gene may be responsible for this association, we performed a transcriptome-wide association study (TWAS) of OS in White patients taking Par-4 dependent chemotherapies. Higher UACA gene expression was significantly associated with OS (P = 4.68 x 10-7), the only gene reaching transcriptome-wide significance (P < 4.34 x 10-6). These results suggest that higher UACA expression may inhibit Par-4 induced apoptosis and lead to stronger chemoresistance and worse survival. We attempted to validate our findings in the independent KPNC Genetic Epidemiology Research on Aging (GERA) cohort. The GERA cohort included only 168 White patients with incident breast cancer after DNA collection who received Par-4 dependent chemotherapies. We found a non-significant association (hazard ratio (HR) = 1.46, P = 0.66) consistent with Pathways Study findings. However, the GERA cohort also included 1,983 prevalent breast cancer patients with biospecimen collection after diagnosis. In this group, the risk allele frequency in breast cancer survivors receiving Par-4 dependent chemotherapies was significantly lower than that in the White population (P = 5.50 x 10-3) while the risk allele frequency in the those not receiving these chemotherapies was similar to the population (P = 0.07). This is consistent with Pathways Study observations that the UACA locus risk allele significantly increased risk of mortality in patients taking Par-4 dependent chemotherapies. A higher mortality in breast cancer survivors carrying the risk allele would result in decreased risk allele frequency. We further validated our findings in Shanghai Breast Cancer Survival Study (SBCSS)and Shanghai Breast Cancer Study, which were conducted from 1996 to 2006 in urban Shanghai and recruited 5,575 breast cancer patients. In this independent Asian breast cancer population, the UACA locus was modestly associated with OS in the overall population (HR = 1.18, P = 0.012), and more significantly in 1,289 SBCSS patients who received anthracyclines (HR = 1.66, P = 1.55 x 10-4). This is the first human study suggesting the Par-4 pathway affects breast cancer patient survival with UACA a key modulator of treatment outcomes by anti-Her2 therapy and doxorubicin. Our findings suggest a path toward new predictive pharmacogenetic markers for personalized medicine targeting the Par-4 pathway for breast cancer treatment. Citation Format: Lawrence H Kushi, Qianqian Zhu, Emily Schultz, Jirong Long, Janise M Roh, Emily Valice, Cecile A Laurent, Li Yan, Isaac J Ergas, Warren Davis, Dilrini K Ranatunga, Marilyn L Kwan, Ping-Ping Bao, Wei Zheng, Xiao-Ou Shu, Christine B Ambrosone, Song Yao. Genome-wide association study identifies UACA as a modulator of breast cancer chemoresistance and survival [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr GS2-05.