Tumour genomic profiling and liquid biopsy are tests that read the genes of a cancer, to find the changes in its DNA that make it grow. Profiling usually reads a piece cut out of the tumour. A liquid biopsy reads the same genes from an ordinary blood sample instead. Doctors use these tests to choose a treatment, to spot a cancer that has come back, and, more and more, to screen people who have no symptoms.
A cancer grows because some of its genes have changed. These changes are called mutations. Different mutations respond to different medicines. For instance, some lung cancers carry a change in a gene called EGFR. For these patients, a tablet that blocks EGFR often works far better than standard chemotherapy. Medicines like this, chosen for a particular mutation, are called targeted therapies. So before choosing a treatment, the oncologist, the cancer specialist, needs to know which mutations the tumour has.
The traditional test uses tissue. A doctor takes a small piece of the tumour, called a biopsy. The lab extracts DNA from it and reads tens or hundreds of cancer-related genes on a DNA sequencer. Software then compares the result with normal DNA, lists the mutations and matches each one to the medicines that act on it. This is an application of genomics.
A liquid biopsy uses blood instead. Tumours shed tiny fragments of their DNA into the bloodstream. A tube of blood holds a very small amount of this tumour DNA, mixed with a great deal of normal DNA. The sequencer reads the fragments many times over, and the software picks out the rare fragments that carry cancer mutations.
Take the case of a 61-year-old woman in Chennai with advanced lung cancer. Her tissue biopsy was too small for genetic testing, and a second biopsy would mean another procedure. So her oncologist sends a blood sample for a liquid biopsy instead. Ten days later, the report shows an EGFR mutation. She starts an EGFR-blocking tablet rather than chemotherapy. Six months later, a repeat blood test looks for the same mutation. If the tumour DNA comes back in her blood, the cancer may be growing again, sometimes before a scan can show it.
Many of these tests were first built on data from patients in America and Europe, and the common mutations differ between populations. So some companies now build profiling tests and gene databases for Indian patients. The tests are still expensive for most Indian families.
The report reaches the hospital EHR through the laboratory information system. With the patients' names removed, results are also pooled in a real-world evidence (RWE) platform, to study which treatments work best for which mutations. The newest use is to screen healthy people for many cancers at once with one blood test. Whether this saves lives, at a cost that health systems will pay, is still an open question.