title: Progesterone receptor isoform-specific promoter methylation: association of PRA promoter methylation with worse outcome in breast cancer patients.
abstract: OBJECTIVE
  ERα and PR levels are critical determinants for breast cancer prognosis and response to endocrine therapy. Although PR is known to be silenced by methylation of its promoter, few studies have correlated methylation with PR levels and outcome in breast cancer. There is only one previous small study comparing methylation of the two PR isoforms, PRA and PRB, which are expressed from different promoters, and finally, there is no prior knowledge of associations between isoform-specific methylation and outcome.
  
  
  METHODS
  We conducted a cohort-based study to test for associations between PRA and PRB methylation, expression, and clinical outcome in tamoxifen-treated patients (n = 500), and in patients who underwent surgery only (n = 500). Methylation and PR levels were measured by bisulfite pyrosequencing and ligand-binding assay, respectively.
  
  
  RESULTS
  Low PR levels were significantly associated with worse outcome in all patients. PRA and PRB promoters were methylated in 9.6% and 14.1% of the breast tumors, respectively. The majority (74%) of PR-negative tumors were not methylated despite the significant inverse correlation of methylation and PR levels. PRA methylation was significantly associated with PRB methylation, although a subset of tumors had PRA only (3.9%) or PRB only (8.3%) methylated. Methylation of PRA, but not PRB was significantly associated with worse outcome in the tamoxifen-treated group.
  
  
  CONCLUSIONS
  Mechanisms other than promoter methylation may be more dominant for loss of PR. Isoform-specific methylation events suggest independent regulation of PRA and PRB. Finally, this article shows for the first time that PRA methylation plays a unique role in tamoxifen-resistant breast cancer.
authors: University of Pittsburgh, 204 Craft Avenue, Pittsburgh, PA 15213, USA.
authors: Thushangi N
authors: TN
authors: Pathiraja
authors: Priya B
authors: PB
authors: Shetty
authors: Jaroslav
authors: J
authors: Jelinek
authors: Rong
authors: R
authors: He
authors: Ryan
authors: R
authors: Hartmaier
authors: Astrid L
authors: AL
authors: Margossian
authors: Susan G
authors: SG
authors: Hilsenbeck
authors: Jean-Pierre J
authors: JP
authors: Issa
authors: Steffi
authors: S
authors: Oesterreich
mesh_terms: D000328:Adult; D000368:Aged; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000188:drug therapy / Q000235:genetics / Q000401:mortality / Q000503:physiopathology*; D019175:DNA Methylation; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D023061:Gene Order; D006801:Humans; D008875:Middle Aged; D011379:Prognosis; D011401:Promoter Regions, Genetic / Q000235:genetics*; D020033:Protein Isoforms / Q000378:metabolism; D011960:Receptors, Estrogen / Q000235:genetics; D011980:Receptors, Progesterone / Q000235:genetics / Q000378:metabolism*; D016019:Survival Analysis; D013629:Tamoxifen / Q000627:therapeutic use; D016896:Treatment Outcome
chemical_list: D018931:Antineoplastic Agents, Hormonal; D020033:Protein Isoforms; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D013629:Tamoxifen