Table 1.

Endocrine resistance in metastatic breast cancer (MBC)1

Primary endocrine resistance	Relapse within 2 years of adjuvant ET PD within first six months of first-line ET for MBC
Secondary endocrine resistance	Relapse while on adjuvant ET but after the first two years or relapse within 12 months after completing adjuvant ET PD≥6 months after initiating ET for MBC

ET, endocrine therapy; PD, progressive disease.