1. A method of developing a gene expression profile indicative of the presence or stage of a selected a disease, disorder or genetic pathology in a mammalian subject comprising: generating a first array of expression levels of a plurality of genes obtained from a biological sample of a subject having said disease, disorder or genetic pathology, wherein said sample contains immune cells or cancer cells, by analyzing expression of said genes in comparison to expression of said genes from a healthy subject; applying penalized discriminant analysis to said first array by comparison to a second array of expression levels of a plurality of genes obtained from a biological sample of a healthy control or a from disease control having a different disease, disorder or genetic pathology; applying recursive feature elimination to said first array to identify and eliminate the least informative up-regulated and down-regulated genes from said comparison; optionally repeating said analysis and elimination steps to obtain a gene expression profile containing a statistically significant number of genes that vary in expression from the expression thereof in the array of said healthy or disease control, wherein said gene expression profile is a characteristic of said selected disease, disorder or genetic pathology or a stage of said selected disease, disorder or genetic pathology.