Table 1.

NRs in Breast Cancer

Nuclear Receptor	Expression in Breast Cancer	NR Activation—Phenotypes
		Proliferation	Apoptosis	Relevance to Breast Cancer Therapy
Steroid Hormone Receptors
ER-α	Overexpression common ∼70%	Proproliferative	Antiapoptotic	Expression determines utility of therapy with SERM or AI (3)
ER-β	Not routinely assessed; likely low	Antiproliferative	Unknown	Increased expression may be a favorable marker (27,28)
PR-A	Expression frequent with ER-α	Proproliferative	Antiapoptotic	May be regulated by ER-α and reflect Tam sensitivity (50)
PR-B	Not routinely assessed	Unknown	Unknown	High PR-A:PR-B ratio increases relapse risk with Tam Rx (48)
AR	Overepression ∼48%–78%	Antiproliferative	Unknown	Appears to be favorable when expressed (48)
GR-α	Overexpression ∼50%	Antiproliferative	Antiapoptotic	Unknown
Coregulators
AIB1/SRC-3	Overexpression (amplification)	Proproliferative	Unknown	High expression may promote Tam resistance (38)
N-CoR	Variable	Antiprolferative	Unknown	Low N-Cor is associated with shorter relapse-free survival (38)
PPARs
PPAR-α	Unknown	Proproliferative	Unknown	Unknown
PPAR-β/δ	Unknown	Proproliferative	Antiapoptotic	Unknown
PPAR-γ	Overexpression	Antiproliferative	Proapoptotic	Increased PPAR-γ expression correlates with survival (83)
RAR and RXR
RAR-α	Variable	Antiproliferative	Unknown	The synthetic RAR ligand, fenritinide, reduces second breast cancers in premenopausal women (111)
RAR-β	Down-regulated	Antiproliferative	Unknown
RAR-γ	Variable	Antiproliferative	Unknown	Unknown
RXRs	Variable	Antiproliferative	Proapoptotic	Unknown
VDR
VDR	Variable	Antiproliferative	Proapoptotic	Vitamin D and calcium intake may inversely correlate with the risk of breast cancer in women (103)
Orphan Receptors (ERRs)
ERR-α	Overexpression	Proproliferative	Unknown	Correlated with overexpression of Her2 and poor prognosis (126)
ERR-β	Overexpression	Unknown	Unknown
ERR-γ	Overexpression	Proproliferative	Unknown	Correlated with hormonally responsive ER/PR positivity (125)

Tam, Tamoxifen; Rx, therapy.