Background: Loss of the stromally-restricted homeodomain transcription factor, Alx4, causes defective mouse mammary epithelial morphogenesis.

Aims: To begin to define the role of ALX4 in the human breast and in breast cancer, the expression pattern of ALX4 in the normal human breast and changes in expression in breast cancer were determined.

Methods: Cells expressing ALX4 in the human breast were identified by co-immunofluorescence using α-ALX4 antibodies and markers of specific mammary cell types. ALX4 expression in breast cancer was then determined by immunohistochemistry on tumour sections that also harboured regions of normal breast tissue. Using criteria that required ALX4 staining in both stromal and epithelial cells, changes in ALX4 expression in tumours on a tissue microarray were determined.

Results: ALX4 was expressed in both stromal and luminal epithelial cells in the human breast. Scoring tissue sections of duct carcinoma in situ (DCIS) or invasive ductal carcinoma (IDC) that also harboured regions of normal breast tissue, a loss of ALX4 (p<0.001) in stromal and epithelial cells in breast tumours was observed. Analysis of ALX4 expression in 123 sections on a tissue microarray confirmed a highly significant loss (p<0.001) of ALX4 in breast cancer in the tumours themselves and in adjacent stromal cells.

Conclusions: These data show a distinct pattern of expression of ALX4 in the human breast relative to the murine mammary gland. Furthermore, characterisation of ALX4 in breast cancer showed that loss of ALX4 in tumours and the surrounding untransformed stroma is a basic characteristic of DCIS and IDC.