Abstract PD4-12: Clustering of activated proteins of the PI3K and MAPK pathways distinguishes ER+/HER2- primary breast cancer patients with preferential tamoxifen benefit

Abstract

Abstract Background Several (activated) proteins of the phosphatidylinositol-3-kinase (PI3K) and/or mitogen-activated protein kinase (MAPK) pathway have been analyzed for an association with adjuvant tamoxifen benefit in estrogen receptor-positive (ER+), HER2-negative (HER2-) breast cancer. Currently, no single protein has yielded convincing results allowing clinical implementation. Combining activated proteins could provide more robust predictive potential. We used unsupervised hierarchical clustering of 7 activated proteins downstream in these pathways, discriminated by expression profile, to analyze adjuvant tamoxifen benefit in ER+/HER2- postmenopausal breast cancer patients. Further, we developed a classification tool based on the generated heatmap groups by pathway activation status to categorize future patients into sensitive for or resistant to adjuvant tamoxifen. Methods Primary tumor blocks from 489 ER+/HER2- (stage I-III) postmenopausal patients previously randomized between tamoxifen (1 to 3 years) vs no adjuvant therapy (IKA trial 1982-1993; Beelen et al, Breast Cancer Res, 2014) were used for immunohistochemistry on tissue microarrays. Median follow-up of the patients without a recurrence event was 8.5 years. Scoring of PTEN, p-AKT(Thr308), p-AKT(Ser473) and p-p70S6K(Thr389) was by cytoplasmic intensity (0-3), p-4EBP1(Ser65) and pERK1/2(Thr202/204) by percentage of tumor cells with positive nuclear staining and p-S6RP(Ser235/236) by the percentage of tumor cells with positive membranous staining. Unsupervised hierarchical clustering was performed on tissue from 293 patients with informative data on all 7 proteins. Cox models were used to assess tamoxifen benefit (defined as the Hazard ratio (HR) of tamoxifen treatment vs no adjuvant therapy for recurrence-free interval) and to compare this benefit between subgroups generated by clustering as well as generated by the classification tool. Cox models included covariates (age, histological grade and subtype, tumor size, PR status) and were stratified for lymph node status. Results Two distinct groups were identified based on hierarchical clustering: one with preferentially activated pathway markers (A) and one with relatively no activation (N). Patients in group N derived significant benefit from tamoxifen (multivariable HR 0.28, 95% CI 0.14 − 0.56, p = 0.000324), while patients from group A had no benefit (multivariable HR 1.57, 95% CI 0.44 – 5.56, p = 0.482), p for interaction 0.018. Contradictory, patients in group A had a better prognosis compared to those in group N (multivariable HR 0.17, 95% CI 0.04 − 0.7, p = 0.014). The classification tool was also successful in differentiating ER+/HER2- patients with or without tamoxifen benefit (p for interaction = 0.016). Conclusions Hierarchical clustering of PI3K/MAPK pathway proteins is able to differentiate patients with adjuvant tamoxifen benefit and patients who would potentially need alternative treatment, for instance with inhibitors of the PI3K or MAPK pathway. The classification tool distinguishing patients with and without tamoxifen benefit should be validated in an independent cohort of postmenopausal patients with primary ER+/HER2- breast cancer. Citation Format: Kruger DT, Beelen K, Opdam M, Sanders J, van der Noort V, Boven E, Linn SC. Clustering of activated proteins of the PI3K and MAPK pathways distinguishes ER+/HER2- primary breast cancer patients with preferential tamoxifen benefit [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD4-12.