Biomarkers for cancer risk, early detection, and prognosis: the validation conundrum.

Successful deployment of early detection technologies to population-based screening for colon, cervix, and, arguably, breast cancer has been responsible for recently observed reductions in disease-associated mortalities from these common malignancies, which are uniformly fatal in their advanced stages. With the advent of highthroughput technologies capable of interrogating genes, proteins, and their associated pathways, the promise of new, inexpensive molecular products for use in cancer early detection and cancer risk assessment has generated scientific enthusiasm. This enthusiasm has attracted substantial public and private resources aimed at discovering molecular products that can form the basis of simple, inexpensive, reproducible, highly sensitive, and specific tests capable of detecting malignancies before their metastatic dissemination. Two important reviews in this issue of Cancer Epidemiology, Biomarkers & Prevention (1, 2) address the historical origins, current progress, future promise, and challenges to this rapidly developing field.