α-Lactalbumin is not a marker of human hormone-dependent breast cancer

Abstract

It has been proposed that milk protein gene expression in human breast carcinomas may indicate a functional oestrogen receptor mechanism, and may therefore be diagnostic of tumours responsive to endocrine therapy¹. Unfortunately this has not been proved, largely because of inconsistencies in the immunoassay procedures used to identify milk proteins, in particular α-lactalbumin, in tissue extracts or serum^1–12. Alternative procedures include the identification of milk protein mRNA by cell-free protein synthesis¹³, and the identification of milk protein RNA transcripts by hybridization to a sequence-specific probe. Here we describe experiments using α-lactalbumin cDNA probes, purified using recombinant plasmids¹⁴, which demonstrate that although polyadenylated and non-polyadenylated α-lactalbumin transcripts are present in normal human mammary tissue during pregnancy and lactation, α-lactalbumin transcripts are not detectable in the human tumour tissues studied. These experiments do however show that a peptide, which shares antigenic determinants with human α-lactalbumin is present in some breast tumour tissues.