Sustaining health in the southern hemisphere.

The human c-myc proto-oncogene is the genomic homologue of the transforming sequences found in MC29, an avian retrovirus that can cause myelocytomatosis, carcinoma, sarcoma and lymphoma (Graf & Beug, 1978; Enrietto et al., 1983). Alterations in the structure or expression of c-myc have been associated with several forms of neoplasia including avian leukosis virus induced B-cell lymphoma, rodent plasmacytoma and human Burkitt's lymphoma, leukaemia, colon carcinoma and variant small cell lung cancer (Hayward et al. In a study of adenocarcinoma of the colon and rectum we have shown significantly elevated expression of c-myc in the majority of tumours, although no evidence of rearrangement or amplification of the gene could be demonstrated (Erisman et al., 1985). In the course of these studies on unselected tumours we have observed that elevated expression of the myc gene occurs more frequently in tumours of the left side (rectum, sigmoid, and descending colon) than in tumours of the right side (caecum and ascending colon). We discuss this finding in view of published reports of similar asymmetries in site distribution in inherited forms of colon cancer. Figure 1 shows a dot blot analysis of the myc RNA level in several colorectal adenocarcinomas and in samples of nearby uninvolved tissue. Expression of myc in a sample is designated as significantly elevated (patients 2,3,4 and 8 in Figure 1) if the myc signal (panel A) is at least 5-fold elevated compared to normal colonic mucosa. This is outside of the range of experimental error as described previously (Rothberg et al., 1984). Hybridization of an identical dot blot with a human c-myc probe reveals no consistent difference between tumour and normal tissue for this oncogene and demonstrates that all lanes have roughly equal amounts of hybridizable RNA (Figure 1, panel B). Table I shows the site distribution of unselected tumour samples with and without elevated expression of c-myc RNA. There is a significant correlation of elevated myc expression with carcinoma of the left side. Tumours of the right side are less likely to contain a significantly elevated level of myc RNA. Chi square analysis of the data in which the null hypothesis states that the tumours from either side form one population with respect to elevated myc expression is rejected at the p <0.025 level (using Yates correction). Other clinical parameters such as Dukes stage and histological appearance of the tumour, the level of serum carcinoembryonic antigen, age and …