Persistent EGFR/K-RAS/SIAH pathway activation drives chemo-resistance and early tumor relapse in triple-negative breast cancer

Abstract

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype. It disproportionately affects BRCA mutation carriers and young women, especially African American (AA) women. Chemoresistant TNBC is a heterogeneous and molecularly unstable disease that challenges our ability to apply personalized therapies. With the approval of immune checkpoint blockade (ICB) for TNBC, the addition of pembrolizumab to systemic chemotherapy has become standard of care (SOC) in neoadjuvant systemic therapy (NST) for high-risk early-stage TNBC. Pembrolizumab plus chemotherapy significantly increased the pathologic complete response (pCR) and improved event-free survival in TNBC. However, clinical uncertainties remain because similarly treated TNBC partial responders with comparable tumor responses to neoadjuvant therapy often experience disparate clinical outcomes. Current methods fall short in accurately predicting which high-risk patients will develop chemo-resistance and tumor relapse. Therefore, novel treatment strategies and innovative new research initiatives are needed. We propose that the EGFR-K-RAS-SIAH pathway activation is a major tumor driver in chemoresistant TNBC. Persistent high expression of SIAH in residual tumors following NACT/NST reflects that the EGFR/K-RAS pathway remains activated (ON), indicating an ineffective response to treatment. These chemoresistant tumor clones persist in expressing SIAH (SIAH^High/ON) and are linked to early tumor relapse and poorer prognosis. Conversely, the loss of SIAH expression (SIAH^Low/OFF) in residual tumors post-NACT/NST reflects EGFR/K-RAS pathway inactivation (OFF), indicating effective therapy and chemo-sensitive tumor cells. SIAH^Low/OFF signal is linked to tumor remission and better prognosis post-NACT/NST. Therefore, SIAH is well-positioned to become a novel tumor-specific, therapy-responsive, and prognostic biomarker. Potentially, this new biomarker (SIAH^High/ON) could be used to quantify therapy response, predict chemo-resistance, and identify those patients at the highest risk for tumor relapse and poor survival in TNBC.

Keywords: EGFR/K-RAS/SIAH pathway activation in TNBC; Triple-negative breast cancer (TNBC); and treatment optimization; chemo-resistance; detection of chemo-resistance; neoadjuvant chemotherapy prognosis; patient risk stratification; precision quantification of therapy efficacy; seven in absentia (SINA) and human homologs of SINA (SIAH) E3 ligase; ubiquitin-mediated proteolysis.

Figure 1

SIAH is the most conserved downstream signaling gatekeeper in the EGFR/K-RAS/SIAH pathway, whose persistent activation is driving TNBC malignancy, tumor relapse, and metastasis. (A) SIAH is the most evolutionarily conserved and the most downstream signaling module identified in the EGFR/K-RAS signaling pathway thus far. (B) Loss of SIAH expression (SIAH^Low/OFF) after effective NACT is correlated with EGFR/K-RAS pathway inactivation and tumor regression/remission, whereas persistent SIAH expression (SIAH^High/ON) after ineffective NACT is correlated with EGFR/K-RAS pathway activation and tumor progression/early relapse. Persistent high SIAH expression (SIAH^High/ON) in high-risk residual tumors post NACT is correlated with EGFR/K-RAS pathway activation, chemo-resistance, and early tumor relapse. (C-D) TNBC tumors were stained with H&E, SIAH, Ki67, phospho-ERK, and EGFR. SIAH outperforms Ki67. SIAH is prognostic and Ki67 is not prognostic in NACT-treated high-risk and locally advanced breast cancer. We found that SIAH^Low/OFF post-NACT correlates with tumor remission and prolonged survival (Alive at 5 years) (C). We found that persistent SIAH^High/ON expression in residual tumors post-NACT is associated with tumor relapse and poor survival (Dead before3-5 years) (D). (E) SIAH1 and (F) SIAH2 are extraordinarily conserved across metazoan species. Conclusion: We found that SIAH^ON/OFF expression is a binary code that reflects tumor-driving EGFR/K-RAS/SIAH pathway activation^ON/inactivation^OFF in TNBC primary and residual tumors As such, SIAH is strategically well positioned to become a new TNBC target, and a new tumor-specific, therapy-responsive, and prognostic biomarker to risk-stratify pIR patients, detect the emergence of treatment-refractory tumors, quantify NACT/NST efficacy, augment RCB classifications, forecast early relapse, and predict patient survival in real time in the clinic. SIAH: Human homologs of Drosophila Seven In Absentia (SINA); NACT: neoadjuvant chemotherapy; RCB: residual cancer burden; TNBC: triple-negative breast cancer.

Figure 2

SIAH marks proliferating tumor cells at a single-cell resolution, and SIAH is a therapy-responsive and prognostic biomarker that can be used to risk-stratify incomplete responders in NACT/NST-treated high-risk and locally advanced breast cancer. IMPAX stands for the IMPAX digital mammography, a powerful diagnostic platform for breast imaging at the Sentara Breast Centers. (A) pCR is a good prognostic marker associated with long-term survival post-NACT/NST. However, for the pIR patients with residual disease, additional tools are needed to distinguish which patients are at high risk for early tumor relapse and thus who may need additional adjuvant chemotherapies. (B) The pIR patients with no or low SIAH expression in residual tumors post-NACT/NST stayed in remission and have prolonged survival (examples: patients #82 and #28). (C) In contrast, the pIR patients with persistent high SIAH expression in residual disease post-NACT/NST developed early relapse and succumbed to their chemoresistant and metastatic diseases (examples: patients #109 and #129). Conclusion: We propose that persistent high SIAH expression in residual tumors is associated with early tumor relapse and poor prognosis, while no or low SIAH expression in residual tumors is associated with tumor remission and good prognosis post-NACT/NST. SIAH: Human homologs of Drosophila Seven In Absentia (SINA); Pir: pathologic incomplete response; NACT: neoadjuvant chemotherapy; NST: neoadjuvant systemic therapy; PCR: athologic complete response.