Claudins (CLDN) are tight junction proteins
which contribute to the paracellular transport and ionic
permeability of various epithelia. In recent years they came
into focus for their suggested role in carcinogenesis and
possible role in cancer therapy. According to our previous
studies, in breast tissue CLDN4 is also related to the level
of cellular differentiation. Thirty-eight estrogen (ER) and
progesterone receptor (PgR) negative, HER2/neu negative,
but cytokeratin 5/6 positive basal-like—mainly grade 3—
breast carcinomas were compared with twenty-one grade 1,
twenty-five grade 2 and twenty grade 3 non-basal-like
invasive breast carcinomas, in respect to their CLDN4 expression. The immunohistochemical reactions were evaluated
both semiquantitatively and by morphometrical
analysis. Statistically significant difference (p=0.001) was
observable regarding CLDN4 expression in the basal-like
group as compared to grade 1 and 2 cancers. Further,
CLDN4 expression was significantly higher (p=0.017) in
the basal-like compared with the non-basal-like grade 3
carcinomas. Our results suggest that basal-like carcinomas
are a subset of breast cancer with high level of CLDN4
protein expression. The finding is in accordance with our
former observation that CLDN4 is indeed related to cellular
differentiation. This observation may be seen as a further
proof that basal-like carcinomas represent a separable group
amongst grade 3 breast carcinomas