Protein kinase C (
PKC) eta is a PKC
isoform whose upregulation is associated with differentiation in many epithelial tissues, including the rat mammary gland. The purpose of this study was to examine whether
PKC eta is altered, in expression or localization, in human
breast cancer.
Paraffin sections of 49 in situ breast lesions, 29 invasive
breast tumors, and nine normal breast biopsies were examined for
PKC eta expression by immunohistochemistry. Adjacent regions of normal epithelium, and in situ lesions that were present adjacent to invasive lesions were also analyzed. In normal epithelium, regardless of the presence of adjacent in situ or invasive lesions,
PKC eta was present in the cytoplasm of the
luminal epithelium, and increased in areas of normal lobular development, similar to normal rat mammary gland.
PKC eta staining intensity was homogeneous in normal lobules, but heterogeneous in in situ and invasive lesions, being focally increased in cells with aberrant nuclear morphology. In situ lesions were similar to adjacent normal epithelium in average staining intensity, regardless of whether invasion was also present. However, the invasive lesions themselves were significantly decreased in staining intensity compared to adjacent in situ lesions. In addition, 75% of invasive
breast cancer lesions showed decreased staining relative to adjacent normal epithelium, compared to 37% of in situ lesions. The invasive
tumors which possessed high
PKC eta staining were associated with positive lymph node status. These results demonstrate that quantitative and qualitative alterations in
PKC eta occur in human breast
cancers.