Clinico-pathological characteristics and claudin 1 protein levels in human breast tumors.

ER α and PR status, determined by the ligand binding assay (ER+, >3fmol/mg protein; PR+, >10fmol/mg protein), tumor size, grade and nodal status were obtained from the Manitoba Breast Tumor Bank. Claudin 1 protein levels were evaluated by immunohistochemistry. H scores: % claudin 1 positive tumor cells multiplied by the intensity of staining (scale 1–3). H scores were further categorized as 0–15 = —(neglible); 20–75 = + (low); 80–150 = ++ (moderate); 155–300 = +++ (high). There was a trend towards high claudin 1 levels (3/4) being associated with ER- tumors, as previously described [18], but no direct correlation with transcript variant and ER status was evident.