Classification of PR-positive and PR-negative subtypes in ER-positive and HER2-negative breast cancers based on pathway scores.

<bold>Purpose: </bold>PR loss in ER+/HER2- breast cancer indicates worse prognosis and insensitivity to anti-estrogen therapy, while the mechanisms of PR loss in ER+/HER2- breast cancer remain unrevealed.<bold>Methods: </bold>In this study, ER+/PR+/HER2- and ER+/PR-/HER2- breast cancer cases from TCGA were used. 1387 pathways were analyzed and used as variables for classifying the two groups with LASSO regression.<bold>Results: </bold>ER+/PR+/HER2- and ER+/PR-/HER2- breast cancer groups can be classified by a combination of 13 pathways using their activity score. Among the 13 pathways, those involving growth factors and ion-channel transporters were most significant in the distinction, followed by pathways involving immune modulation and cell metabolism. Two growth factor pathways, EGF and IGF-1, were deferentially regulated in ER+/PR+/HER2- and ER+/PR-/HER2- groups.<bold>Conclusions: </bold>In conclusion, this study indicated in ER+/HER2- breast cancers the various status of PR expression can be an indication of molecular variation, particularly for the growth factor pathway activation. [ABSTRACT FROM AUTHOR]