The understanding that human neoplasms are clonal cell proliferations ultimately derived from a single transformed somatic cell represents a major advance in cancer biology. A cell population is designated as clonal if it can be demonstrated to have arisen from a single parent or progenitor cell. The clonality of select human neoplastic cell populations can be determined in several ways. One way is by detection of stable, unique somatic chromosome abnormalities (Philadelphia chromosome; 8, 21 translocation); somatic gene mutations (H-ras); or immunoglobulin heavy/light chain rearrangements. The drawbacks of these are that they either are rare, are fortuitous, or require labor-intensive techniques. Another way to assess clonality in human cell populations is to exploit the unique position of the X chromosome in human female development.
