Table 1.

Identification of resistance

Mechanism	Phenotype	Assessment
Inherent resistance	ER negativity	ER measurement
	Defective ER	ER read-outs
	Alternative growth signalling	GF/receptor assays
ER modified	ER phosphorylation	Phosphorylation status
	ER co-activators	ER read-outs
	ER co-repressors
Ineffective treatment	Inherent lack of potency	Target read-outs
	Compensatory mechanisms	Target read-outs
	Poor pharmacokinetics	Pharmacogenetics

ER, oestrogen receptor; GF, growth factor.