The potential role far prolactin-inducible protein (PIP) as a marker of human breast cancer micrometastasis

The prolactin-inducible protein (PIP/GCPD15) is believed to originate from a limited set of tissues, including breast and salivary glands, and has bee n applied as a clinical marker for the diagnosis of metastatic tumours of u nknown origin. We have investigated the potential role of PIP mRNA as a mar ker of human breast cancer metastasis. Using reverse transcription polymera se chain reaction and Southern or dot blot analysis, PIP mRNA was detected in 4/6 breast cell lines, independent of oestrogen receptor (ER) status. In breast primary tumours (n = 97), analysed from histologically characterize d sections, PIP mRNA was detected in most cases. Higher PIP mRNA levels cor related with ER+ (P = 0.0004), progesterone receptor positive (PR+) (P = 0. 0167), low-grade (P = 0.0195) tumours, and also PIP protein levels assessed by immunohistochemistry (n = 19, P = 0.0319). PIP mRNA expression was also detectable in 11/16 (69%) of axillary node metastases. PIP mRNA expression , however, was also detected in normal breast duct epithelium, skin, saliva ry gland and peripheral blood leucocyte samples from normal individuals. We conclude that PIP mRNA is frequently expressed in both primary human breas t tumours and nodal metastases. However, the presence of PIP expression in skin creates a potential source of contamination in venepuncture samples th at should be considered in its application as a marker for breast tumour mi crometastases. (C) 1999 Cancer Research Campaign.