Cells exfoliated from colorectal cancers may only be implicated in local recurrence if they are proven to be viable and capable of growth. Thirty patients with primary colorectal cancer were studied. Cells were obtained from primary tumour, uninvolved mucosa, mesorectum, lumen of the bowel, luminal mucus, serosal surface of the bowel and from washings of the tumour bed after dissection. Colonies grew in vitro in monolayer culture from 21/30 primary tumours; 11/41 mesorectum specimens; 11/27 luminal washings; 14/29 luminal mucus specimens; 1/27 serosal surface washings and 3/13 post-dissection washes. Colonies stained positively for the epithelial markers cytokeratin and desmosomes and also for carcinoembryonic antigen. Cells capable of in vitro growth are present in these various sites and, if spilled at operation, may well be implicated as one of the factors leading to local recurrence.

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Metabolic labelling with [35S]methionine and immunoprecipitation with specific antibodies to bovine desmosomal glycoproteins 2 and 3 (dg2 and dg3: desmocollins) reveals a triplet of polypeptides of Mr 115,000, 107,000 and 104,000 in MDCK cells. Tunicamycin treatment shows that this heterogeneity does not arise through differential N-linked glycosylation. Under conditions in which cells are actively forming desmosomes, the largest polypeptide, dg2, becomes phosphorylated on serine, but the two smaller polypeptides, dg3a and 3b, do not. Controlled trypsinisation of intact cells yields three membrane-protected fragments (Mr 28,000, 24,000 and 23,000) derived from these glycoproteins. The largest of these fragments is phosphorylated but the two smaller fragments are not. A monoclonal antibody to bovine dg2 and dg3 stains MDCK cells cytoplasmically. In immunoblotting of MDCK cells the monoclonal antibody recognises dg2 strongly and shows a weaker reaction with a band of lower Mr corresponding to dg3a. It also recognises the immunoprecipitated 28,000 Mr fragment from trypsinised cells and a smaller fragment of 24,000 Mr. The simplest interpretation of these data is that all three glycoproteins have a transmembrane configuration with a single membrane-spanning domain, and show heterogeneity of size and phosphorylation in their cytoplasmic domains. The data are discussed in relation to the known structures of some cell adhesion molecules. Questions about the relative roles and distributions of the different polypeptides in desmosomal organisation are raised.