I am affiliated with a company that has just introduced a laboratory test to identify the tissue of origin for metastatic cancers. In November 2007, a team of neurosurgeons presented a poster at the Society for Neuro-Oncology meeting describing their success in using this test to evaluate eight unknown primary cancers found in the brain. I thought this might be useful new information for this discussion. A copy of the poster is at:
http://www.pathworkdx.com/news/SNO_Pathwork_Stanford_Brain_P
Hope this helps.