In general, better correlation has been observed between patient outcome and molecular or IHC detection of tumor cells in the bone marrow compared to blood.4,30,39,40 It is possible that circulating cells have the ability to get into the bloodstream but lack the ability to survive at a metastatic site, while cells in the marrow are at an "advanced" stage in the metastatic continuum, having acquired the capacity to survive in the circulation, attach, and grow in a remote environment. This, however, is speculation until we better understand the molecular events underlying the meta-static process.

While few studies using single markers have shown results that correlate with clinical or pathologic parameters, correlation with survival/outcome was observed using IHC to detect cytokeratin-positive cells in bone marrow samples from breast cancer patients.30 Similar findings have been reported for prostate39 and colorectal cancer.41 In the United States, such studies can be hampered by clinical practices that do not include bone marrow sampling as part of routine staging for many tumors.

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