Genes are hereditary material that are transferred from parents to their children. Chromosomes are the basic genetical material in human cells and there are 23 pairs of chromosomes in each cell. The human genome project revealed that there are around 20,000 protein coding genes present in our chromosomes. These gene and their products regulates the growth and development of the human body.
Any change in these sequences can initiate abnormal growth that may lead to cancer. Cancer cells undergo some genetic changes leading to tumor formation. It invariably occurs in every cancer, whether it is lung, breast, or prostate cancer. Identification of such genetic changes can help the healthcare providers in early detection, and even in treatment of the cancers.
Gene sequencing is a method that helps determine abnormal genetic changes. Profiling of genetic sequence in cancer cells can give us valuable clues. Such profiling is useful for monitoring cancer progression and detecting actionable changes in therapy. Currently available techniques, such as liquid biopsy and other commercial tests, can only profile a small portion of the human genome. Moreover, previously only biopsy of cancer tissue was used for gene sequencing, which is an invasive and difficult procedure. Recent advances in medical science inform that dying cancer cells also shed genetic material into blood, termed circulating tumor DNA. So, blood samples collected from cancer patients may be a potential source of material for genetic sequencing.
A recent study applied a new technique that used a high-sequencing approach, to evaluate the gene sequence in length and breadth. The approach helped scan a very larger area of the human genome (508 genes, 2 million base pairs) yielding accurate results and generating 100 times more data than the conventional approach. The study also evaluated blood samples as a potential material for gene sequencing. It included 161 patients with metastatic breast, lung, or prostate cancer, and collected tissue or blood from each of them. The tissue samples were analysed by MSK-IMPACT™, a 410-gene diagnostic test and the white blood cell from blood sample were sequenced using high-intensity 508-gene sequencing assay.
The study results showed that almost 90% of the patients had at least one genetic change in the tissue sample, and the change was also found in the provided blood sample. Researchers also detected a total of 864 genetic changes in tissue samples and 627 changes in the blood samples. The more important finding was that three-fourths of the actionable genetic changes found in tissue samples, were also found in the blood samples.
The lead author of the study Dr. Pedram Razavi was excited about the study finding and said that “Our findings show that high-intensity circulating tumor DNA sequencing is possible and may provide invaluable information for clinical decision-making, potentially without any need for tumor tissue samples”. He also mentioned that “Our combined analysis of cell-free DNA and white blood cell DNA allows for identification of tumor DNA with much higher sensitivity, and deep sequencing also helps us find those rare tumor DNA fragments.”
This is a ground-breaking study towards early detection of cancer and an important step in the process of developing blood tests for cancer patients.
1. New Technology Dives Deep Into the Cancer Genome [Internet]. ASCO. 2017 [cited 2017 Jun 24]. Available from: http://www.asco.org/about-asco/press-center/news-releases/new-technology-dives-deep-cancer-genome
2. How many genes are in the human genome? [Internet]. [cited 2017 Jun 24]. Available from: http://www.edinformatics.com/math_science/human_genome.htm