c-myc protein product is a marker of DNA synthesis but not of malignancy in human gastrointestinal tissues and tumours.

c-myc is a conserved cellular gene. The gene product is a nuclear-bound 62,000 molecular weight phosphoprotein (p62c-myc). Although p62c-myc levels have been measured in colorectal cancers, little is known about the expression of the protein in upper gastrointestinal tumours and tissues. Studies were performed on tumour and mucosal specimens from 87 patients with colorectal cancer, from two with polyposis coli, from six with squamous oesophageal carcinomas and from 18 with gastric carcinomas. The mean p62c-myc content was measured in units of fluorescence in the G1 diploid and G2 diploid peaks of the cell cycle by multiparameter flow cytometry using the 6E10 antibody. The nuclear p62c-myc content increased with DNA synthesis in tumours and mucosa. G2 levels of p62c-myc were higher in glandular mucosa than in adenocarcinomas. No differences in peak nuclear c-myc expression were found in relation to histological grade or to anatomical site of colorectal tumours. There was a broadly inverse relationship between G2 p62c-myc levels in tumours and mucosa and their in vivo 5-bromo-2'-deoxyuridine labelling indices. Nuclear p62c-myc levels are cell cycle related but the protein has not been shown to be a marker of increased tissue proliferation or of gastrointestinal malignancy. The reduction of the nuclear p62c-myc content of many adenocarcinoma cells compared with glandular mucosa cells suggests that reduced synthesis or nuclear retention of the normal protein may be a factor in the development of gastrointestinal adenocarcinomas, although the mechanism by which this may occur is not clear.