9. Oestrogen & Anti-Oestrogens

• Oestrogen


  The predominant intracellular oestrogen is 17β-estradiol (E2), which is secreted primarily by the granulosa cells in the ovaries during the menstrual cycle

  
• Ovarian production of oestrogen

  Regulated by the hypothalamic-pituitary-ovarian (HPO) axis
• Oestrogen biosynthesis in postmenopausal women

  Mediated by aromatase, which is found in adipose tissue as well as other organs
• During ovulation, E2 production rises dramatically by 8- to 10-fold
• Oestrogen biosynthesis


  1. Begins by anterior pituitary release of luteinising hormone (LH) and follicle-stimulating hormone (FSH) in response to the hypothalamic peptide gonadotropin-releasing hormone (GnRH)

  2. LH stimulates androgen production, whereas FSH upregulates aromatase, which catalyses the rate-limiting and final step of oestrogen biosynthesis: the aromatisation of androgen to oestrogen

  3. High levels of oestrogen in turn act via negative feedback to dampen oestrogen production to inhibit the release of GnRH, LH, and FSH
• Breast changes during menstrual cycle

  • Cyclical changes occur in the breast during menstruation
  • Premenstrual swelling and tenderness of both breasts occurs during the second half of the menstrual cycle
  • The breast are least engorged 7-10 days after the beginning of menses
• Oestrogen


  Mammary ducts enlarge and proliferate during luteal phase
• Progesterone


  • Growth of lobules and alveoli
  • Breasts increase in size, tenderness, and retains more fluid

  
• In pre-menopausal women, the main source of oestrogen is the ovary
• In post-menopausal women, oestrogen is derived from the conversion of androgens into oestrogens
• Aromatase


  The main enzyme involved in oestrogen biosynthesis, belonging to the cytochrome P450 family and is predominantly located in the liver, adrenal glands and fatty tissue
• Oestrogen Receptor (ER)


  • Oestrogen binds to ER
  • Homodimers bind to DNA
  • Activate ER regulated genes
  • Synthesis of ER associated proteins
• ER is expressed in normal breast epithelial cells
• 70% of breast tumours show high expression of ER
• ER positive tumours are associated with negative nodal status and low tumour grade
• ER expression correlates with improved overall survival and disease free survival
• Anti-oestrogens


  • Tamoxifen (Nolvadex®)
  • Fulvestrant
• Only 60% ER positive tumours respond to endocrine treatment
• Tamoxifen


  • Blocks oestrogen as a selective estrogen-receptor modulator (SERM)
  • Been in use for over 40 years to treat ER+ positive early, locally advanced and metastatic breast cancers
  • Used in pre- and peri-menopausal women with ER+ breast cancer
  • Use for 5 years increases overall survival in women with ER+ breast cancer
• Tamoxifen mechanism


  1. Both E2 and tamoxifen bind to ER and lead to dimerisation, conformational change in the activating function-2 (AF2) domain of ER and binding to oestrogen-response elements (EREs)

  2. The conformational change with tamoxifen is different from that with E2 and leads to persistent but less efficient transcription of most oestrogen-dependent genes
• Aromatase Inhibitors


  • Prevents peripheral conversion to oestrogens in post-menopausal women
  • In postmenopausal women with oestrogen-receptor positive invasive breast cancer who are at medium or high-risk of disease recurrence, an aromatase inhibitor should be given as first-line therapy
• Exemestane (Aromasin)


  • Steroidal compound that forms covalent bonds with aromatase which is irreversible and can only be overcome by the synthesis of new enzyme
  • Blocks the conversion of testosterone into E2 and androstenedione into E1
  • Inhibition of aromatase occurs through covalent bonding
• E2 and tamoxifen


  Bind to ER and lead to dimerisation, conformational change in the activating function-2 (AF2) domain of ER and binding to oestrogen-response elements (EREs)
• Conformational change with tamoxifen

  Different from that with E2 and leads to persistent but less efficient transcription of most oestrogen-dependent genes
• Aromatase Inhibitors


  • Prevents peripheral conversion to oestrogens in post-menopausal women
  • In postmenopausal women with oestrogen-receptor positive invasive breast cancer who are at medium or high-risk of disease recurrence, an aromatase inhibitor should be given as first-line therapy
• Exemestane (Aromasin)


  • Steroidal compound that forms covalent bonds with aromatase which is irreversible and can only be overcome by the synthesis of new enzyme
  • Blocks the conversion of testosterone into E2 and androstenedione into E1
  • Inhibition of aromatase occurs through competitive binding of aromatase to the heme group of cytochrome P450, decreasing oestrogen biosynthesis in the peripheral tissues of the body and in the breast
• Anastrozole (Arimidex) and Letrozole (Femara)

  • Competitive AIs with reversible action
  • Bind reversibly to aromatase by competing with the endogenous ligands for the active site of aromatase
  • Forms a non-covalent reversible bond to the haem iron atom in the active site
• ER testing of invasive breast cancers


  • Standard assay for predicting which patients may benefit from endocrine therapy
  • Several different scoring systems although there is no internationally accepted scoring method
• ER immunohistochemistry


  • IDC: 90 –95% Intensity: High
  • IDC: 50 –75% Intensity: Medium
  • IDC: 0% Intensity: Negative
• ER positive


  • 1% to 100% of tumour nuclei positive
  • Endocrine therapy benefit for cancers with 1% to 10% of cells staining ER positive is limited
• ER negative


  < 1% or 0% of tumour cell nuclei are immunoreactive
• Progesterone


  • Has differentiation and proliferative roles in the adult breast
  • PR is a surrogate marker of ER activity in breast cancer
  • ER+ tumours can be PR+ or PR-
• ER/PR subtypes


  • Key markers to classify subtypes of breast cancer with different treatment needs
  • PR is measured in the same way as ER by immunohistochemistry
  • ER+ tumours with lower or negative PR expression have a worse prognosis
• ER/PR status


  • Defines different treatment needs in breast cancer
  • Endocrine Responsive Positive: Endocrine therapy alone
  • Endocrine Response Uncertain Low Positive: Endocrine therapy benefit from adding chemotherapy
  • Endocrine non-responsive Negative: Chemotherapy alone, no benefit from endocrine therapy
• Oncotype DX Breast Recurrence Score Test

  • 21-Gene Panel Used to Calculate Recurrence Score - 16 cancer genes and 5 reference genes
  • PCR based assay on FFPE material
  • Categories: Low risk (RS <18), Int risk (RS ≥18 and <31), High risk (RS ≥31)
• Oncotype DX B-20 Results: Tam vs Tam + Chemo

  • Low RS: No benefit
  • Int RS: No benefit
  • High RS: 28% absolute benefit from tam + chemo