Alteration of
psoriasin (S100A7) expression has previously been identified in association with the transition from preinvasive to invasive
breast cancer. In this study we have examined persistence of
psoriasin mRNA and
protein expression in relation to prognostic factors in a cohort of 57 invasive
breast tumors, comprising 34 invasive
ductal carcinomas and 23 other invasive
tumor types (lobular, mucinous, medullary, tubular). We first developed an
IgY polyclonal chicken antibody and confirmed specificity for
psoriasin by Western blot in transfected cells and
tumors. The
protein was localized by immunohistochemistry predominantly to epithelial cells, with both nuclear and cytoplasmic staining, as well as occasional stromal cells in psoriatic skin and
breast tumors; however, in situ hybridization showed that
psoriasin mRNA expression was restricted to epithelial cells. In
breast tumors, higher levels of
psoriasin measured by
reverse transcriptase-polymerase chain reaction and Western blot (93% concordance) were significantly associated with
estrogen and
progesterone receptor-negative status (P < 0.0001, P = 0.0003), and with nodal
metastasis in invasive ductal
tumors (P = 0. 035), but not with
tumor type or grade.
Psoriasin expression also correlated with inflammatory infiltrates (all
tumors excluding medullary, P = 0.0022). These results suggest that
psoriasin may be a marker of aggressive behavior in invasive
tumors and are consistent with a function as a
chemotactic factor.