Background: The importance of KAI1 to colorectal cancer (CRC) progression is unclear, with conflicting data regarding changes in KAI1 expression during tumour progression.
Materials and methods: In situ hybridisation and immunohistochemistry, with a semiquantitative scoring system, were used to assess KAI1 mRNA and protein levels, respectively, in normal colon samples (43), and non-metastatic (24) or metastatic (33) primary cancers, and liver metastases (48).
Results: There was significant loss of KAI1 mRNA and protein staining in non-metastatic primary tumours versus normal tissues (Bonferroni, p < 0.05) but levels recovered to near normal in metastatic primary tumours and liver metastases. Increased KAI1 expression significantly correlated with distant metastases (Mann-Whitney, p = 0.0001, mRNA; p = 0.033, protein), cancer-specific survival (Cox regression analysis p = 0.0002, mRNA; 0.0493, protein) and overall patient survival (p = 0.0001, mRNA). Multivariate analysis (Cox proportional hazards model) confirmed high KAI1 mRNA expression was an independent prognostic indicator of distant metastasis (p < 0.0001), cancer-specific survival (p < 0.0001) and overall patient survival (p < 0.0001).
Conclusion: These data indicate a complex relationship between KAI1 and progression of human CRC, in which expression is reduced in localised primary tumours, but regained in disease associated with metastasis.