The locus of the polymorphic epithelial mucin (PEM) tumour antigen on chromosome 1q21 shows a high frequency of alteration in primary human breast tumours

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Abstract
Tumour and blood leukocyte DNAs from sporadic breast cancer patients were examined for chromosome 1 loss of heterozygosity using a probe for a polymorphic epithelial mucin, PEM, which is expressed in >92% of breast carcinomas as well as in normal lactating breast tissue. Expression is detected by the monoclonal antibodies (MAbs) HMFG‐1,‐2 and SM‐3 which react with epitopes in the 20 amino‐acid repeat unit of the core protein. The PEM probe has been mapped to the chromosome band 1q21, a region that is often incriminated in chromosomal rearrangements in breast tumours. Loss of heterozygosity or alteration at the PEM locus was detected in 34% of the 70 informative patients examined. Twenty of the 24 individuals showed loss of an allele, whereas 4 showed gain of an additional allele or amplification of an existing allele. Twenty‐eight percent of informative cases exhibited alterations at the MS32 locus, 1q42–43, and 20% had alterations at the short arm locus MSI at 1p33–35. These findings identify the long arm of chromosome 1 and in particular the region around the PEM gene for localization of a gene whose loss or alteration may, in some tumours, contribute to the progression of disease in breast cancer patients.