Among cancer’s mysterious phenomena is a tumors’ ability to metastasize while they remain too small to be detected, and the growth of metastases after the primary tumor has disappeared altogether.  These scenarios obscure the cancer’s original site, raising a large obstacle for chemotherapy, which is based on knowing the original tissue.  Some genetic tests are now available, though, that have enhance ability to identify tumor origins based on gene expressions.  “The Tissue of Origin” test from Pathworks Diagnostics  (Sunnyvale, CA) takes 1,500 gene expressions into account, and compares expression levels of the unknown specimen to those of  known levels from study sets.  Tumors of unknown origin only make up between 2% and 5% of all cancers, but even so, their total comes to about 30,000 cases which is more than liver or bone cancers.         MORE