MUC1
glycoprotein is overexpressed and its intracellular localization altered during
breast carcinoma tumorigenesis. The present study aimed to clarify the relationship of cytoplasmic localization of MUC1 with the
breast cancer subtype and the correlation of 10 molecules associated with cell polarity in
breast cancer subtypes. We immunostained 131
formalin-fixed and
paraffin-embedded
breast cancer specimens with an anti-MUC1 antibody (MUC1/CORE). For 48 of the 131
tumor specimens,
laser-assisted microdissection and real-time quantitative RT-PCR were performed to analyze
mRNA levels of MUC1 and 10 molecules, β-
catenin,
E-cadherin,
claudin 3,
claudin 4,
claudin 7, RhoA, cdc42, Rac1, Par3 and Par6. Localization of MUC1
protein varied among
breast cancer subtypes, that is, both the apical domain and cytoplasm in
luminal A-like
tumors (P < 0.01) and both the cytoplasm and cell membrane in
luminal B-like (
growth factor receptor 2 [HER2]+)
tumors (P < 0.05), and no expression was found in triple negative
tumors (P < 0.001).
Estrogen receptor (ER)+ breast
cancers showed higher MUC1
mRNA levels than ER- breast
cancers (P < 0.01). The incidence of mutual correlations of expression levels between two of the 10 molecules (55 combinations) was 54.5% in normal breast tissue and 38.2% in
luminal A-like specimens, 16.4% in
luminal B-like (HER2+), 3.6% in HER2 and 18.2% in triple negative specimens. In conclusion, each
breast cancer subtype has characteristic cytoplasmic localization patterns of MUC1 and different degrees of disrupted correlation of the expression levels between the 10 examined molecules in comparison with normal breast tissue.