Introduction: Insulin-like growth factor 1 (IGF-1)/IGF-1 receptor (IGF-1R) signalling is activated in breast cancer and asso-ciated with disease progression. Pregnancy-associated plasma protein-A (PAPP-A) is a metalloproteinase that can cleave IGFbinding proteins leading to the release of bioactive IGF-1 and the subsequent activation of IGF-1 signalling. Here, we aimed toassess the prognostic significance of PAPP-A in breast cancer.Methods: Breast cancer tissue microarrays were stained for PAPP-A and expression correlated with survival and other clinicalfeatures. Analysis of publicly available data sets was carried out to determine associations between PAPPA and gene sets associ-ated with IGF-1/IGF-1R pathway activation.Results: PAPP-A was expressed in both the tumour and stromal compartments in breast cancer specimens and was higher inoestrogen receptor (ER)-negative (ER-) than ER-positive (ER+) cases. There was a significant association between high PAPP-Aexpression and reduced cancer-specific survival (CSS) in ER+ (HR 1.389, 95% CI 1.051–1.836, p = 0.021) but not ER- patients (HR1.040, 95% CI 0.712–1.598, p = 0.838). In a second cohort of ER+ invasive lobular carcinoma (ILC) PAPP-A expression was alsoassociated with reduced CSS (HR 1.765, 95% CI 1.098–2.836, p = 0.019). PAPPA correlated with REACTOME PI3K-AKT andIGF1R signalling gene sets in ER+ breast cancers.Conclusion: High expression of PAPP-A is associated with poor prognosis in ER+ breast cancer and correlates with IGF-1/IGF-1R pathway activation
