Comparison between aromatase inhibitors and sequential use

J Steroid Biochem Mol Biol. 2003 Sep;86(3-5):275-82. doi: 10.1016/s0960-0760(03)00367-4.


The biochemical efficacy of aromatase inhibitors and inactivators in vivo may be determined by two types of methods; by measuring plasma or tissue estrogen levels, or assessment of the conversion of the androgen substrate (in practice, androstenedione) into estrogens (estrone) by the use of tracer methods. While methods to determine plasma and tissue estrogens are limited through lack of sensitivity required to measure the very low concentrations recorded in postmenopausal women on treatment with these compounds, measurement of in vivo aromatization is an extensive procedure, applicable to a limited number of patients only. While we may correlate the mean level of aromatase inhibition achieved with different compounds to clinical efficacy, data correlating individual estrogen suppression to clinical outcome among patients treated with a specific compound is limited. The now well-characterized phenomenon of lack of cross-resistance between non-steroidal aromatase inhibitors and steroidal aromatase inactivators are likely due to biochemical effects not related to differences in total body aromatase inhibition.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Aromatase Inhibitors*
  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / enzymology
  • Breast Neoplasms / metabolism
  • Clinical Trials, Phase III as Topic
  • Drug Resistance, Neoplasm
  • Endpoint Determination
  • Enzyme Inhibitors / metabolism
  • Enzyme Inhibitors / pharmacology*
  • Enzyme Inhibitors / therapeutic use*
  • Estradiol / blood
  • Estrone / analogs & derivatives
  • Estrone / blood
  • Humans
  • Randomized Controlled Trials as Topic / methods
  • Treatment Outcome


  • Aromatase Inhibitors
  • Enzyme Inhibitors
  • Estrone
  • Estradiol