Abstract P3-12-02: Loss of PTEN expression, <i>PIK3CA</i> mutations, and breast cancer survival in the Nurses’ health studies
Authors: Tengteng Wang, Yujing J Heng, Gabrielle M Baker, Vanessa C Bret-Mounet, Susan E Hankinson, Michelle D Holmes, Wendy Y. Chen, Walter C. Willett, Bernard A. Rosner, Rulla M Tamimi, A. Heather Eliassen
Journal: Cancer Research (2022)

Abstract Background: PTEN loss and/or PIK3CA mutation are hypothesized to predict more aggressive tumor behavior and worse outcomes in women with breast cancer. However, the results of previous studies with small sample size have been conflicting. Methods: We followed pre- and postmenopausal women with invasive breast cancer from the Nurses’ Health Study (diagnosed 1976-2011) and Nurses’ Health Study II (1989-2011) with data available on PTEN cytoplasmic expression (n=4316, breast cancer-specific deaths=777) and/or PIK3CA mutation (n=2930, breast cancer-specific deaths=317). PTEN protein expression was evaluated by immunohistochemistry and scored as a digitally quantified continuous measure (1-100%). Polymerase chain reaction and pyrosequencing of six hot spot mutations of PIK3CA were performed on DNA extracted from formalin-fixed paraffin-embedded tumors. Information on other covariates was self-reported at baseline and repeatedly measured with follow-up questionnaires every two to four years. Multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between loss of PTEN expression and/or PIK3CA mutation and breast cancer-specific mortality were estimated using Cox proportional hazards regression models. Results: In this large epidemiological study, the loss of tumor cell PTEN cytoplasmic staining expression (≤10%) occurred in 17.6% of cases, and the overall mutation of PIK3CA occurred in 10.8% of cases. After adjusting for tumor characteristics, treatment, and lifestyle factors, the loss of PTEN expression (versus expression &amp;gt;10%) was not associated with worse breast cancer survival among overall samples (HR =0.85; 95%CI=0.71-1.03) and among estrogen receptor (ER)-positive tumors (HR =1.11; 95%CI=0.84-1.47). However, among women with ER-negative tumors, PTEN expression loss was strongly associated with lower breast cancer mortality (HR =0.68; 95%CI=0.48-0.96). Overall mutation status of PIK3CA was not associated with breast cancer mortality (HR =1.06; 95%CI=0.78-1.45). Combining PTEN and PIK3CA status, compared with tumors without PTEN loss and without PIK3CA mutation (wild type), those with PTEN loss and/or PIK3CA mutation were not at higher risk (HR =1.05; 95%CI=0.85-1.32). However, women with PTEN loss and PIK3CA mutation jointly (n=39, breast cancer-specific deaths=15) had increased breast cancer mortality (HR =2.05; 95%CI=1.07-3.94). Conclusion: This study is the largest to date examining PTEN and PIK3CA status and breast cancer survival, in which we found that the prognostic value of PTEN status differed by ER status, and the joint status of PTEN loss of expression and PIK3CA mutation was associated with worse breast cancer survival. Citation Format: Tengteng Wang, Yujing J Heng, Gabrielle M Baker, Vanessa C Bret-Mounet, Susan E Hankinson, Michelle D Holmes, Wendy Y. Chen, Walter C. Willett, Bernard A. Rosner, Rulla M Tamimi, A. Heather Eliassen. Loss of PTEN expression, PIK3CA mutations, and breast cancer survival in the Nurses’ health studies [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-12-02.