Table 1.

Alterations in the PI3K signaling pathway (adapted from [12, 16])

Gene	Aberration	Effect on signaling	Frequency			Prognosis
			HR-positive/luminal	HER2-positive	TNBC/basal-like
ERB2	gene amplification or overexpression	hyperactivation of Erb2 signaling (PI3K, MEK)	10	100	0	correlates with poorer outcome
PTEN	loss of function/reduced expression	hyperactivation of PI3K signaling	29–44	22	67	no consistent correlation
PIK3CA	activating mutation	hyperactivation of PI3K signaling	28–47	23–33	8	ER+/HER2−, better outcome; ER+/HER2+, poorer outcome
PIK3CB	amplification	unknown				unknown
IGF1R, INSR	receptor activation	activates IGF-1R/InsR signaling (PI3K, MEK)	41–48	18–64	42	unknown
FGFR1	amplification	hyperactivation of FGFR signaling (PI3K, MEK)	8.6–11.6	5.4	5.6	correlates with shorter RFS
INPP4B	reduced expression or genomic loss	hyperactivation of PI3K signaling	8	38	88	correlates with poorer outcome
AKT1	activating mutation	hyperactivation of Akt signaling	2.6–3.8	0	0	unknown
AKT2	amplification	hyperactivation of Akt signaling	2.8			unknown

EGFR = Epidermal growth factor receptor, ER = estrogen receptor, FGFR = fibroblast growth factor receptor, HER2 = human epidermal growth factor receptor 2, HR = hormone receptor, IGF-1R = insulin-like growth factor-1 receptor, InsR = insulin receptor, MEK = MAPK/ERK kinase, mTORC1 = mammalian target of rapamycin complex 1, PI3K = phosphatidylinositol 3-kinase, RFS = relapse-free survival, TNBC = triple-negative breast cancer.