What more of us means.

The human gene sequences encoding the translation-associated functions of a-subunit of elonga-tion factor 1 (EF-la) and the ubiquitin carboxyl extension protein (HUBCEP80) have been isolated by differential cDNA screening, and found to have significantly higher levels of expression in fibroadenomas (benign) compared with carcinomas (malignant) of the breast. These data parallel our previous findings that the acidic ribosomal phosphoprotein P2 also has higher expression levels in the benign breast tumours (Sharp et al., 1990). In situ hybridisation has shown these genes to be expressed predominantly in the epithelium of breast tumours. Metastasis is a complex process which involves both the dissemination of tumour cells from the site of the primary tumour and their subsequent establishment at a distant site. In breast cancer metastasis is the primary cause of death, but there is great diversity in the clinical course of the disease and metastases may not become evident for up to 25 years (Brinkley & Haybittle, 1975; Blamey et al., 1979). Assays to identify which tumours have greater metastatic potential would be of benefit in the design of therapeutic regimes, since absence of metastases at time of presentation is a good prognostic indicator (Fisher et al., 1984). Tumour progression may involve genetic changes or alterations which affect the expression of specific genes. Metastasis of certain tumours has been related to secreted proteinases also correlate with metastatic capacity. However, no single marker has been identified which distinguishes between metastasising and non-metastasising cells of a specific organ, let alone between tumours arising in different sites. Differential screening of cDNA libraries has been used successfully by several groups to identify genes which have altered expression patterns between malignant and non-malignant tumours. One example of such a gene is NM23, first isolated by differential screening of K-1735 murine mela-noma cell lines with varying metastatic potentials, where higher expression of NM23 was shown to be associated with low metastatic potential (Steeg et al., 1988). It was subsequently found that NM23 gene expression in 71 human primary breast carcinomas was inversely correlated with histopathological indicators of metastatic potential, including number of involved lymph nodes and tumour grade, and positively associated with longer disease-free interval and overall survival (Hennessy et al., 1991). The NM23 protein has high (77%) homology to a Dictyostelium nucleoside diphosphate kinase Gipl7 (Wallet et al., 1990). Similarly, two novel genes WDNM1 and WDNM2 have been isolated from the rat mammary adenocarcinoma cell line DMBA-8 …