Molecular methods have proven extremely useful for the detection of occult tumor cells and can yield valuable clinical information as well as a better understanding of the mechanisms of metastasis and relapse of cancer (1). In the case of many hematopoietic malignancies, the presence of a unique molecular marker such as a chromosomal translocation has made this task relatively straightforward. Carcinomas generally lack such markers, however. Certain oncogene mutations have been targeted, but the lack of consistent and specific markers has remained problematic.