A standardized assay to identify colon cancer genotypes by in vitro tetraploidy in human dermal fibroblasts.

Increased tetraploidy in dermal fibroblast cultures (IVT), which is a putative biomarker for genetic predisposition to colon cancer, was assayed by two different methods: by per cent of tetraploid metaphases in chromosome preparations from non-confluent monolayer petri dish cultures in logarithmic growth (MA); by flow cytometry (FCM) distribution of DNA content of propidium iodide stained cells from plastic flask cultures in stationary growth phase. The assayed cultures were derived from split thickness skin biopsies from two clinical groups: 11 normal individuals without a family history of colon cancer and 17 clinically affected individuals with autosomal dominant polyposis coli cancer syndrome (6 with colonic adenomatosis, i.e. familial polyposis coli (FPC) and 11 also having extracolonic lesions, i.e. the Gardner syndrome, (GS). Concordance was observed between the two assays. There was a linear relationship between the per cent of tetraploid metaphases assayed in the chromosome preparations and the per cent of cells with a DNA index (DI) of precisely 2, or of all cells with a DI greater than 1 as determined by FCM. In comparisons between the clinical groups, there was significant differences in the FCM DNA index (p values less than 0.001) of IVT- (normals and IVT- FPC) and IVT+ individuals (IVT+ GS and those FPC with IVT). The per cent of cells with a DI of 2 and greater than 1 could be used to distinguish all IVT- individuals (normals and IVT- FPC) from IVT+ FPC individuals. However, only by per cent of cells with a DI greater than 1 could all the individual GS affecteds be distinguished from IVT- individuals. Thus, the per cent of cells with a DI greater than 1 is considered to be the parameter of choice to be used in assaying IVT by flow cytometry.