Purpose: Poly(adenosine diphosphate-ribose) polymerase (PARP) plays a key role in DNA repair and cellular stress response. Inhibitors of PARP show promising clinical activity in metastatic, triple-negative or BRCA-mutated breast cancer.
Patients and methods: We investigated cytoplasmic PARP (cPARP) and nuclear PARP (nPARP) expression by immunohistochemistry in 638 pretreatment biopsies from patients on the GeparTrio study and evaluated its predictive and prognostic value after neoadjuvant anthracycline/taxane-based chemotherapy.
Results: cPARP expression was high in 23.7%, intermediate in 50.9%, and negative in 25.4% of tumors. High cPARP expression was significantly correlated with nonlobular histology (P < .001), undifferentiated grade (P < .001), positive nodal status (P = .049), and negative hormone receptor (HR) status (P < .001) but not with human epidermal growth factor receptor 2 (HER2) status. Expression was high in 35.5% of triple-negative tumors, 24.6% of HER2-positive tumors, and 18.0% of HR-positive/HER2-negative tumors (P < .001). Pathologic complete response (pCR) rates were 26.5%, 19.1%, and 8.0% in patients with high, intermediate, or negative expression, respectively (P < .001). This predictive effect was most prominent in HR-positive tumors (P = .035) or HER2-negative tumors (P < .001). High cPARP expression was a negative, but not independent, prognostic factor for disease-free survival (DFS; P = .0025) and overall survival (OS; P = .0022). cPARP expression was highly prognostic in patients without a pCR (DFS, P < .001; OS, P < .001) and in patients with HR-positive tumors (DFS, P < .001; OS, P < .001). No such correlations were found for nPARP expression.
Conclusion: High cPARP expression correlates with aggressive tumor pattern and predicts high sensitivity to neoadjuvant taxane/anthracycline-based chemotherapy but also unfavorable long-term prognosis. As a potential target for PARP inhibitors, cPARP-positive breast cancer might become a new, clinically relevant entity.