Prognostic impact of PIK3CA protein expression in triple negative breast cancer and its subtypes

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Abstract
Background Triple negative breast cancer (TNBC) harbors a heterogeneous group of carcinomas with poor prognosis and high genetic variability. As a potential aim for targeted therapy, genetic mutations leading to an activation of the phosphoinositide 3-kinase pathway in a catalytic subunit (PIK3CA) in breast cancer have been analyzed currently. Little is known about the clinical impact and prognostic or predictive value of this marker in TNBC subtypes. Methods Samples from 119 TNBC cases were submitted to immunohistochemical PIK3CA protein expression analysis and scored semi-quantitatively as negative, weak (1 +), or strongly expressed (2 +). Expression scores were correlated to patient’s characteristics, imaging features, and TNBC subtypes. TNBC subtypes were categorized into four subtypes: basal like, mesenchymal like, luminal androgen receptor (LAR), and immunomodulatory. Results We did not observe differences in clinical aspects and imaging features between TNBC with and without PIK3CA expression. PIK3CA expression was in general higher in the LAR subtype. The disease-free survival and overall survival were significantly better in TNBC with PIK3CA protein expression, independent of TNBC subtypes. Conclusion Despite conflicting results in the literature, our study clearly shows a better outcome of PIK3CA-expressing TNBC, independent of TNBC subtypes. PIK3CA expression in TNBC is not associated with specific clinical or diagnostic features. Further molecular studies and meta-analysis are warranted to clarify the prognostic and predictive role of PIK3CA protein expression.

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