In regards to drug selection, fluorescent In-Situ Hybridization (FISH) is used to examine gene copy number variation in the tumor. Polymerase Chain Reaction (PCR) or DNA sequencing is used to determine gene mutations in the DNA tumor.
FISH overall is a better predictor of benefit, but can only be done with adequate biopsy tissue. Getting tumor cells from blood maybe feasible for solid tumors, though usually only when the tumor is very advanced, and then only in small numbers.
It seems plausible to get enough specimen from circulating tumor cells for solid tumors. It may be possible using PCR or similar technology for specific agents. Only minute quantities of DNA are necessary for PCR. DNA can be amplified from a single cell.
PCR amplification techniques raise considerable concerns regarding contamination from one specimen to another, creating the potential for false positive results. Clinical interpretation of PCR results may also be challenging.
PCR may be useful when culture is difficult due to the low numbers of the organisms, for lengthly culture requirements, or when there is difficulty in collecting an appropriate sample. However, the results would not be indicative of what would happen inside the human body.
They usually proliferate (grow) cancer cells from a small sample and subject those cells to chemo. Cells 'grown' in the lab will not behave the same way as the actual cancer cells do in your body's own environment.
Because they test on subcultured cells (as opposed to fresh tumor cultures) and test the cells in monolayers (as opposed to three dimensional cell clusters), the cell grown in the lab will not behave the same way as the actual cancer cells do in your body's own environment.
This work does not clarify whether a protein inhibitor, as a result of testing for a mutation, is likely to be superior, inferior, or equal to standard chemotherapy in either the good or poor profile groups, which is a pressing clinical question.
Dr. Eric Green, a leader of the genome mapping project, said it will take years to make sense of all the information. Genomics is an information science and we now have information overload, according to Dr. Green. Our ability to generate that information has outpaced our ability to analyze it.
http://cancerfocus.org/forum/showthread.php?t=3348
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