Abstract P2-08-20: Prognostic impact of SRC, CDKN1B and JAK2 expression in metastatic breast cancer patients treated with trastuzumab

Abstract

Abstract Background-aim: SRC, CDKN1B and JAK2 play a crucial role in the coordination and facilitation of cell-signaling pathways controlling a wide range of cellular functions. In the present study, we investigated the prognostic significance and clinical utlity of these biomarkers in metastatic breast cancer (MBC) patients treated with trastuzumab (T). Methods: We assessed SRC, CDKN1B and JAK2 mRNA expression with qRT-PCR (Taqman-MGB assays) on 197 paraffin tumors. PIK3CA mutation status was previously assessed. Relapsed (RMBC) and de novo MBC (dnMBC) patients had received T for metastatic disease only. Tumors were centrally re-assessed for HER2 status. Results: Only 133/197 patients (67.5%) were found to be truly HER2(+). CDKN1B mRNA expression strongly correlated with SRC (rho = 0.71) and JAK2 (rho = 0.54); high CDKN1B was more frequent in RMBC compared to dnMBC (p = 0.001) and in PIK3CA wild-type tumors (p = 0.005). In HER2(+) patients, low CDKN1B conferred higher risk for progression (HR 1.58, 95% CI 1.08-2.32, p = 0.018). In HER2(-) patients, low SRC was associated with longer survival (HR 0.56, 95% CI 0.32-0.99, p = 0.045) and, as a trend, with increased progression-free survival (PFS) (p = 0.067). For PFS, in RMBC, we observed trends for unfavorable low CDKN1B (p = 0.068) and JAK2 (p = 0.086); similarly, in dnMBC for unfavorable low CDKN1B (p = 0.072). Low SRC showed a trend for better survival in RMBC (p = 0.087). Upon multivariable analyses, only PIK3CA mutations strongly predicted for unfavorable PFS in HER2(+) patients (HR 3.37, 95% CI 1.98-5.73, p < 0.001). Low CDKN1B and JAK2 mRNA expression remained unfavorable factors for PFS in dnMBC and RMBC patients (HR 2.36, 95% CI 1.01-5.48, p = 0.046 and HR 1.76, 95% CI 1.01-3.06, p = 0.047, respectively). Conclusions: Low CDKN1B and JAK2 mRNA expression were unfavorable prognosticators in a cohort of T-treated MBC patients previously unexposed to this agent, with distinct impact in de novo and RMBC. Our results highlight biological and clinical differences between de novo and RMBC and suggest that CDKN1B and JAK2, if validated, may serve as prognostic factors potentially implicated in T-resistance, which seems to be associated with distinct pathways in the two MBC settings. Citation Format: Economopoulou P, Kotoula V, Koliou G-A, Papadopoulou K, Christodoulou C, Pentheroudakis G, Koutras A, Bafaloukos D, Papakostas P, Pectasides D, Kotsakis A, Razis E, Samantas E, Kalogeras KT, Economopoulos T, Fountzilas G. Prognostic impact of SRC, CDKN1B and JAK2 expression in metastatic breast cancer patients treated with trastuzumab [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 P2-08-20.