Lung cancer is an uncontrolled cell growth that originates inside the lungs. Over time, these abnormal cells spread to distant organs (metastasis). The cancer cells are like parasites. These compete with the healthy cells and deprive them of nutrition and oxygen, eventually killing them.
Lung cancer patients have better treatment options and survival rates if they are diagnosed early. The five-year survival rate for those diagnosed before the cancer has spread to distant sites is 55 out of every 100.
Given the highest risk factor for lung cancer development is smoking, it is advised that smokers and those at risk due to exposure to environmental pollutants must get regularly screened through a computed tomography (CT) scan. In case the CT scan shows a suspicious spot, the doctor may further recommend a biopsy for making a definitive diagnosis.
Though other potential screening modalities are available to screen for lung cancer, CT scan remains the modality of choice. The sputum cytology, chest ray, and measurement of biomarker levels in the blood or blood tests for lung cancer may be recommended under special circumstances.
Can a Blood Test Detect Lung Cancer?
Though not routinely done, doctors may sometimes do a liquid biopsy or biomarker testing after they have completed a tissue biopsy. The liquid biopsy is a blood test that checks the blood of lung cancer patients for certain substances in the blood called lung cancer markers.
The test is particularly useful in cases of a subtype of lung cancer called the non-small cell lung cancer (NSCLC) type adenocarcinoma. The blood test is based on a simple principle: the cancer cells release a specific mutated deoxyribonucleic acid or DNA (genetic material) into the blood; this is called cell-free DNA. This cell-free DNA shed by cancer tumor cells is captured and tested for specific mutations.
The aim of tissue biopsy or blood tests are
To decide if certain targeted therapies are right for the patient.
To check if the patient's lung cancer has become resistant to the therapy protocol and needs another protocol.
To test a person in whom lung cancer has relapsed for alternative therapy.
Lung cancer treatment options now include several targeted therapies aimed at particular mutations in the cancer cell. Each of these treatments can provide substantial benefits but only to those patients with those specific mutations. The United States Food and Drug Administration approved targeted therapies that are only available for the following mutations in NSCLC:
- EGFR,
- ALK,
- ROS1,
- BRAF V600E,
- NTRK,
- MET, and
- RET.
There are several other biomarkers present in the NSCLC cases, but unfortunately, there are still no targeted treatment approaches for those proteins.
| Percentage of non-small cell lung cancer (NSCLCs) | Genetic mutation | The population that may benefit from screening and approved drug |
|---|---|---|
| 5% of NSCLCs | ALK gene |
|
| 1-2% of NSCLCs | ROS1 gene |
|
| Unspecified cases of NSCLC | RET gene |
|
| About 5% of NSCLCs | BRAF gene |
|
|
Unspecified cases of NSCLC |
MET gene |
|
| Unspecified cases of NSCLC | PD-L1 protein |
|
Other blood tests done in cases of lung cancer are
- Complete blood count (CBC): Checks for the different types of blood cells. This test is repeated regularly during treatment because chemotherapy drugs can affect blood-forming cells in the body.
- Liver function test: This test ascertains if the drugs used as chemotherapy medications are causing liver damage.
- Kidney function test: This is done to check the creatinine, urea, and uric acid levels during chemotherapy.
- Blood calcium: The blood calcium levels may be elevated in some cases of advanced lung cancer (paraneoplastic syndrome). These need to be checked and treated on time.
From 
Cancer Resources
American Cancer Society. Tests for Lung Cancer. https://www.cancer.org/cancer/lung-cancer/detection-diagnosis-staging/how-diagnosed.html#:~:text=Blood%20tests,healthy%20enough%20to%20have%20surgery