Lung cancer can originate from any of the specialized cell types that help make up the lung, and generally fall into one of two categories: small cell lung cancer, or non-small cell lung cancer. Lung cancers can be caused by environmental factors, such as smoking, or genetic factors like inherited genetic mutations. Early detection of lung cancer is associated with better prognosis and more effective treatment. A use of biomarkers to screen for lung cancer allows for detection of tumors. A range of biomarkers have been identified to screen for lung cancer.
Hypermethylation
Hypermethylation occurs when the cell modifies its DNA to change the levels of different proteins present in the cell. Hypermethylation involves adding a chemical onto the DNA that decreases the amount of the protein corresponding to a methylated gene. Essentially, if the cell wants to stop making a specific protein, it can hypermethylate the corresponding gene, and the protein will no longer be made. In cancer, genes responsible for slowing tumor growth are often hypermethylated, and without the tumor suppressor proteins present in cells, the tumor grows and develops.
Hypermethylation can be used as a biomarker for the detection of lung cancer. In a 2006 study published in "PLoS Medicine," Dr. D. Shames found that 132 genes are commonly hypermethylated in lung cancer. Genetic testing and screening to look for hypermethylation of these genes in patients can be used to diagnose lung cancer.
hTERT
hTERT is a protein found in lung cancers that contributes to cell division. Under normal conditions, cells are able to divide a certain number of times, and after they are finished dividing, they enter a stage called senescence. In cancer, the cells never enter senescence, and instead divide indefinitely. The protein that allows for unlimited cell division is called hTERT, which is also known as telomerase. hTERT modifies the DNA within cancer cells, so they are never told to enter senescence.
The presence of hTERT in lung cells can be used as a biomarker for lung cancer, since normal lung cells do not typically express the protein. In a 2008 study published in "Disease Markers," Dr. M. Strazisar reports that testing the levels of hTERT in a lung tumor also helps doctors assess the severity of cancer, since more aggressive lung cancers contain higher levels of the protein. The presence of hTERT may also be used to screen for other forms of cancer.
Missing DNA
As cancer progresses, cells within the tumor divide more and more rapidly, and the result of this rapid cell division is an increase in mutations within the DNA. In severe cancers, cells within the tumor may be missing large chunks of DNA, called chromosomes. The loss of a piece of a chromosome is called a chromosome deletion. The chromosome deletions may be used as biomarkers for lung cancer.
In lung cancer, a number of patients have genetic abnormalities of a specific part of their DNA, in a region called chromosome 3p. In a 2010 study published in "BMC Cancer," Dr. V. Senchenco found that several lung cancer patients have deletions to regions within chromosome 3p, which correspond to the location of genes that prevent lung cancer. The loss of tumor-suppressing genes due to deletion helps drive the progression of lung cancer. Chromosomal deletions in chromosome 3 may be used as a biomarker to indicate lung cancer.
References
- National Institutes of Heath: A genome-wide screen for promoter methylation in lung cancer identifies novel methylation markers for multiple malignancies.
- National Institutes of Health: K-RAS and P53 mutations in association with COX-2 and hTERT expression and clinico-pathological status of NSCLC patients.
- National Institutes of Health: Simultaneous down-regulation of tumor suppressor genes RBSP3/CTDSPL, NPRL2/G21 and RASSF1A in primary non-small cell lung cancer.
