Identification of changes in gene expression associated with minimal residual disease

Minimal residual disease (MRD), the tumour burden which remains after a cou rse of treatment that has resulted in clinical remission [1], appears to di ffer in certain characteristics from the primary tumour population. Certain ly the cells which comprise MRD have had to escape from the constraints of the primary tumour mass, invade normal tissue and penetrate small vessels i n order to enter the circulation in which they then have had to survive. Su ch activities are the consequence of the expression of specific proteins an d these may well be a reflection of alterations in DNA or RNA levels. Ident ifying the changes in RNA expression levels between related cell groups exh ibiting different phenotypes recently has become a great deal easier as a c onsequence of developments in analytical procedures such as Differential Di splay (DD) and Serial Analysis of Gene Expression (SAGE). Application of th ese procedures to MRD cells recovered from blood, bone marrow or lymph node , should identify novel sequences associated with tumour progression and th e development of disseminated disease.