title: High progesterone receptor expression correlates to the effect of adjuvant tamoxifen in premenopausal breast cancer patients.
abstract: OBJECTIVE
  Tamoxifen has long been the drug of choice in adjuvant endocrine therapy of steroid hormone receptor-positive breast cancer, and it still remains important due to its well-documented beneficial effect. Hormone receptor status is often reported as "positive" or "negative" using 10% positive nuclei as a cutoff. In this study, we aimed to assess whether a further subclassification of hormone receptor status could enhance the treatment predictive value.
  
  
  METHODS
  The immunohistochemical expression of estrogen receptor (ER) and progesterone receptor (PR) was quantified in tissue microarrays with tumors from 500 premenopausal breast cancer patients previously included in a randomized trial of adjuvant tamoxifen compared with an untreated control group.
  
  
  RESULTS
  Our findings show a gradually increasing tamoxifen effect in tumors with >10% ER-positive nuclei. However, when analyzing tamoxifen response according to various PR fractions, we found that it was primarily patients with tumors showing >75% PR-positive nuclei that responded to tamoxifen treatment, with an improved recurrence-free [relative risk, 0.42 (0.25-0.70); P = 0.001] as well as overall [relative risk, 0.49 (0.28-0.84); P = 0.010] survival.
  
  
  CONCLUSIONS
  Adjuvant tamoxifen improved recurrence-free and overall survival for premenopausal patients with tumors showing >75% PR-positive nuclei. No effect could be shown in tumors with fewer PR-positive nuclei. The PR was a stronger predictor of treatment response than the ER. Based on these findings, we suggest the implementation of a fractioned rather than dichotomized immunohistochemical evaluation of hormone receptors in clinical practice, possibly with greater emphasis on the PR than the ER.
authors.affiliation: Department of Laboratory Medicine, Division of Pathology, Malmö University Hospital, Lund University, Malmö, Sweden.
authors.forename: Maria
authors.initials: M
authors.lastname: Stendahl
authors.forename: Lisa
authors.initials: L
authors.lastname: Rydén
authors.forename: Bo
authors.initials: B
authors.lastname: Nordenskjöld
authors.forename: Per Ebbe
authors.initials: PE
authors.lastname: Jönsson
authors.forename: Göran
authors.initials: G
authors.lastname: Landberg
authors.forename: Karin
authors.initials: K
authors.lastname: Jirström
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001943:Breast Neoplasms / Q000175:diagnosis / Q000188:drug therapy*; D017024:Chemotherapy, Adjuvant; D018572:Disease-Free Survival; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007150:Immunohistochemistry; D011237:Predictive Value of Tests; D017697:Premenopause; D016032:Randomized Controlled Trials as Topic; D011960:Receptors, Estrogen / Q000096:biosynthesis; D011980:Receptors, Progesterone / Q000096:biosynthesis*; D015996:Survival Rate; D013629:Tamoxifen / Q000627:therapeutic use*; D046888:Tissue Array Analysis; D016896:Treatment Outcome
chemical_list: D000970:Antineoplastic Agents; D011960:Receptors, Estrogen; D011980:Receptors, Progesterone; D013629:Tamoxifen