In addition to new tumour antigens, new prognostic and diagnostic markers are 
needed for common cancers. In this study, we report the expression of Dickkopf-1 
(DKK1) in multiple common cancers. This constitutes a comprehensive analysis of 
the DKK1 expression profile. Dickkopf-1 expression was evaluated by classical 
and quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and 
enzyme-linked immunosorbant assay for protein determination, in cancer lines and 
clinical specimens of several cancer origins. For breast cancer, expression was 
correlated with clinicopathological parameters. Dickkopf-1 expression was 
confirmed in several cancer cell lines derived from breast and other common 
cancers. Dickkopf-1 protein secretion was documented in breast, prostate and 
lung cancer lines, but was negligible in melanoma. Analysis of DKK1 expression 
in human cancer specimens revealed DKK1 expression in breast (21 out of 73), 
lung (11 out of 23) and kidney cancers (six out of 20). Interestingly, DKK1 was 
preferentially expressed in oestrogen and progesterone receptor-negative tumours 
(ER(-)/PR(-); P=0.005) and in tumours from women with a family history of breast 
cancer (P=0.024). Importantly, DKK1 protein production was confirmed in multiple 
breast cancer specimens that were positive by RT-PCR. This work establishes DKK1 
as a potential prognostic and diagnostic marker for cohorts of breast cancer 
patients with poor prognosis. Dickkopf-1 may also become a relevant candidate 
target for immunotherapy of different cancers.