Abstract 5612: Cancer-immune interactions in luminal breast cancers: PI3KCA mutations, PI3K/AKT/mTOR activation and tumor-infiltrating lymphocytes
Authors: Sobral-Leite Marcelo , Salomon Izhar , Opdam Mark , Beelen Karin , Vlierberghe Ronald L. van , Blok Erik J. , Horlings Hugo M. , Sanders Joyce , Vijver Koen Van de , Kuppen Peter J. , Linn Sabine , Schmidt Marjanka K. , Kok Marleen 
Published: July 2017

Introduction: Therapy resistance to adjuvant tamoxifen in estrogen receptor positive (ER+) breast cancer (BC) is related to activation of downstream proteins in the PI3K/AKT/mTOR pathway. However, clinical efficacy of mTOR inhibitors has so far been modest. Growing evidence shows that genomic make-up of cancer cells plays a crucial role in an anti-cancer immune response and this is reflected in the presence of tumor infiltrating immune cells. This begs the need for understanding the relationship between tumor-related immune activity, PIK3CA hot-spot mutations (PIK3CAm) and PI3K/AKT/mTOR pathway activation in ER+BC.

Material and methods: The IKA trial recruited stage I to III postmenopausal BC patients (1982 till 1994), who were randomized to tamoxifen or no adjuvant therapy. Sequenom mass spectrometry-based genotyping was used for PIK3CAm assessment. Immune markers and phosphorylation status of proteins in the PI3K/AKT/mTOR pathway [p-AKT (Thr308 and 473), p-mTOR, p-ERK1/2, p-p-70S6K and p-4EBP1] were assessed by immunohistochemistry and scored by two pathologists. Expression of CD4, CD8 and FOXP3 was evaluated using automatic scoring by image-analysis software (SlidePath® or AxioVision®) and compared with manual scoring by two pathologists. Associations were assessed using multivariable logistic regression models, including as co-variables: age, tumor grade, lymph node status, tumor size, and progesterone receptor and HER2 status.

Results: We included 563 ER+BC cases. PIK3CAm were found in 159 (32%) of the 486 tumors genotyped. On average, PI3K/AKT/mTOR downstream proteins and immune markers were scored in 409 tumors (range: 366 to 438). Stromal CD8 expression, but not CD4 or FOXP3, was significantly higher in PIK3CA mutated tumors (OR=1.11; 95%CI: 1.02-1.22). Stromal FOXP3 expression, but not CD4 or CD8, was significantly increased in tumors with activated proteins from the PI3K/AKT/mTOR pathway (except p-mTOR). The largest association was with p-4EBP1 (OR=1.34; 95%CI: 1.21-1.48) and smallest with p-70S6K (OR=1.15; 95%CI: 1.08-1.22).

Conclusion: In our dataset of ER+BC, PIK3CAm are associated with higher level of CD8+ T cells. Tumors with activation of the PI3K/Akt/mTOR pathway tend to have more FOXP3+ T cells. Together, our results suggest that PIK3CA mutation/activation harbor an immune-related tumor microenvironment.

Citation Format: Marcelo Sobral-Leite, Izhar Salomon, Mark Opdam, Karin Beelen, Ronald L. van Vlierberghe, Erik J. Blok, Hugo M. Horlings, Joyce Sanders, Koen Van de Vijver, Peter J. Kuppen, Sabine Linn, Marjanka K. Schmidt, Marleen Kok. Cancer-immune interactions in luminal breast cancers: PI3KCA mutations, PI3K/AKT/mTOR activation and tumor-infiltrating lymphocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5612. doi:10.1158/1538-7445.AM2017-5612