title: Molecular subgroups of small (pT1) breast carcinomas belonging exclusively to the ductal infiltrating variety.
abstract: BACKGROUND
  The use of microarray technology has resulted in a new classification of breast cancer according to gene expression profiles. None of the reports published so far using this new classification has stratified the studied tumors by histology or size.
  
  
  METHODS
  This study was restricted to the ductal infiltrating variety only, and to pT1 size using the immunohistochemical markers estrogen receptor (ER), progesterone receptor (PR), HER2 and cytokeratin 5/6. ER+ and/or PR+, HER2- tumors were termed "luminal A"; ER+ and/or PR+, HER2+ "luminal B"; triple-negative, CK 5/6+ and/or HER1+ "basal-like"; with an additional category for ER-, PR-, HER2+ tumors termed HER2, and a final group of unclassified ones, negative for all five markers.
  
  
  RESULTS
  Out of 346 tumors, 251 (72.5%) were luminal A, 45 (13%) were "triple-negative" ("basal"-like), 20 (5.8%) were luminal B, and 30 (8.7%) were HER2. Luminal A, "triple-negative" ("basal"-like), and HER2-expressing tumors (luminal B + HER2) showed significantly different associations with histological and nuclear grade, mutant p53 expression and Ki67 labelling index.
  
  
  CONCLUSIONS
  Studies of the other, less frequent histological varieties of breast cancer, stratifying by tumor size, are mandatory to disclose which precise gene-expression pattern defines similar subgroups.
authors.affiliation: Centro de Patologia de la Mama, Universidad Rey Juan Carlos, Facultad de Ciencias de la Salud, Alcorcon, Madrid, Spain. jose.schneider@urjc.es
authors.forename: José
authors.initials: J
authors.lastname: Schneider
authors.forename: Armando
authors.initials: A
authors.lastname: Tejerina
authors.forename: Clemente
authors.initials: C
authors.lastname: Perea
authors.forename: Raúl
authors.initials: R
authors.lastname: Lucas
authors.forename: Jaime
authors.initials: J
authors.lastname: Sánchez
mesh_terms: D001943:Breast Neoplasms / Q000145:classification* / Q000473:pathology*; D018270:Carcinoma, Ductal, Breast / Q000145:classification* / Q000473:pathology*; D004847:Epithelial Cells / Q000473:pathology; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D053555:Keratin-5 / Q000378:metabolism; D053553:Keratin-6 / Q000378:metabolism
chemical_list: D053555:Keratin-5; D053553:Keratin-6