In the past, many tumor marker laboratory tests have not been sensitive enough for the very early detection of cancer. However, many of them have nonetheless proved useful in monitoring therapy, following the course of the tumor, and predicting prog­ nosis. Today, cancer may be viewed as a genetic disease with various specific chromo­ somal and nucleotide aberrations, such as mutations, deletions, gene amplification, gene rearrangements, and translocations occurring during the transformation of a nor­ mal cell into a malignant cell. The considerable advances in technology during the past several years have greatly enhanced our ability to detect human cancers in the very early stages of