BP1, a putative signature marker for inflammatory breast cancer and tumor aggressiveness.

Our previous studies revealed that beta protein 1 (BP1) was barely detectable in normal human breasts, but was seen in 21%, 46%, and 81% of hyperplastic, in situ, and invasive breast lesions, respectively. Our current study attempted to assess BP1 expression in inflammatory breast cancer (IBC), a very aggressive subtype of breast cancers characterized by extensive lympho-vascular invasion and involvement of dermal lymphatics. Paraffin-embedded tissue sections from 45 cases of IBC (nine with paired metastatic lymph nodes) and different controls were assayed immunohistochemically for BP1 expression. Positive BP1 immunoreactivities were present in all IBC cases. Strikingly, all cancer cells metastasized to lymph nodes and cells within lymphatic channels were uniformly and strongly immunoreactive to BP1. The percentage of BP1 positive cells and the intensity of BP1 immunostaining in IBC cases were significantly greater than those in non-IBC cases. Our findings suggest that BP1 may possess properties of onco-proteins that promote tumor progression, invasion, and metastasis, representing a putative signature marker for IBC and tumor aggressiveness.