Two main types of cancer originate in the lungs – non-small cell and small-cell lung cancer.
Cancer may also spread from other parts of the body to the lungs, in which case it’s called secondary lung cancer.
This is the most common type of lung cancer, accounting for over 80% of all lung cancer cases. It multiplies and spreads to other parts of the body slower than small cell lung cancer (SCLC).
NSCLC is classified into three sub-types, depending on the type of cells found in the tumor. They are grouped because the treatment for each type is similar.
Adenocarcinomas develop in the outer parts of the lung, in cells that are responsible for mucus secretion. They are more likely to be diagnosed early, so they have a comparatively high survival rate¹. This is the most prevalent type of non-small cell lung cancer.
More than 40% of lung cancer patients suffer from adenocarcinoma. It is more common in women and can affect young people. Both smokers and non-smokers can get this type of cancer.
The term adenocarcinoma in situ (previously called bronchioloalveolar carcinoma) refers to a localized adenocarcinoma that has been detected early and has not yet spread. It has an excellent prognosis after tumor resection (surgery).
Lung adenocarcinomas which develop in peripheral regions of the lung can often spread to the lymph nodes and beyond, so it is important to know where your adenocarcinoma is situated so that your doctor can monitor the lymph nodes.
Squamous cell carcinoma
This type of lung cancer begins in the flat squamous cells that line the bronchi (large airways) in the lungs. Squamous cell lung cancer accounts for more than 30% of all NSCLC patients, and it's more likely to be found in smokers than non-smokers.
Squamous cell carcinoma does not often metastasize, and if it does, it will spread slowly. It can spread to the brain, bones, adrenal glands, or liver. In its later stages, a squamous cell tumor may grow within the affected lung to form a large cavity of gas or fluid.
Large cell lung cancer
This is a less common type of NSCLC. Large cell lung cancer is sometimes referred to as undifferentiated carcinoma and occurs in any part of the lung. The cancer cells appear large and round under the microscope, and they tend to spread quickly.
Other types of NSCLCs
Two NSCLCs are quite rare:
Adenosquamous carcinoma occurs in only 0.4-4% of non-small cell lung cancers. It contains both adenocarcinoma and squamous cell carcinoma cells, which are present in at least 10% of the tumor.
Sarcomatoid carcinomas are found in only 0.3-3% of all NSCLC patients. This condition is very difficult to treat with conventional chemotherapy and radiotherapy. It has a poor prognosis, although research is ongoing² to find successful treatment approaches.
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Approximately 10-15% of all lung cancers are SCLCs. You may also hear this cancer being called oat cell cancer because of the cells’ appearance when viewed under a microscope.
Small cell lung cancers spread faster than other types of cancer. In about 70% of people diagnosed with this type of cancer, it has spread by the time the cancer is detected. It also metastasizes to other parts of the body quite quickly.
The prognosis of SCLC is poor because it is so aggressive. However, if it has been detected early, it will respond well to chemotherapy and radiation treatments. Surgery is not generally used when treating this type of lung cancer because of the high spread rate.
The chance of reoccurrence of this type of cancer is also high.
A variant of SCLC is combined small cell lung carcinoma or c-SCLC. This is when the malignant tumor contains SCLC components as well as one or more components of NSCLC. Treatment plans are similar to SCLC treatments, although research for better approaches is ongoing.
“Metastatic” means spreading. Metastatic lung cancer occurs when cancer cells from a primary tumor in the lung travel through the blood or lymph systems to other body tissues.
Local metastasis is a term for the spread of the lung cancer cells to a different part of the lung.
Distant metastasis is the term for the spread of lung cancer cells to different parts of the body such as the liver or brain.
The process of metastasis is typically gradual. The cancer cells reproduce and eventually secondary tumors develop. The cancer is still referred to as lung cancer, wherever in the body the new tumors are sited.
Lung carcinoid tumors
These tumors begin in neuroendocrine cells – a type of nerve cell that helps manage levels of oxygen and carbon dioxide in the lungs. Neuroendocrine cells are found in other areas of the body, but only cancer in neuroendocrine cells in the lungs is called a lung carcinoid tumor.
Thankfully, lung carcinoid tumors are rare – fewer than three in 50 lung tumors are of this type.
You may also hear these tumors described by their position in the lungs. Central carcinoids are situated in the walls of the bronchi in the center of a lung. Peripheral carcinoids are found in the bronchioles at the edges of the lungs.
90% of lung carcinoid tumors are classed as typical. They grow slowly and don't tend to metastasize to other parts of the body. They don't seem to be caused by smoking. Atypical carcinoids are less common. They grow and spread more rapidly and may be linked to smoking.
Other neuroendocrine tumors
Other types of neuroendocrine tumors can be diagnosed. They may be classed as a type of small cell lung cancer or a large cell neuroendocrine cancer, which is a kind of NSCLC. Your doctors must know the type of tumor so that they can decide on the right treatment plan.
Other lung tumors
Other rare lung tumors are:
Adenoid cystic carcinoma (ACCL). This is a rare type of tumor that often develops in the salivary glands but can occur in other parts of the body such as the lung. When it is situated in the lung, surgery may be the best option.
Primary pulmonary sarcoma (PPS) is a very rare type of non-epithelial malignant tumor. Sarcomas in the lungs have often spread from cancerous cells in other parts of the body.
Primary pulmonary lymphoma (PPL) is also very rare. It can affect one or both lungs. Lymphomas in the lungs are more likely due to Hodgkin’s disease or a non-Hodgkin’s lymphoma.
Benign lung tumors are often referred to as “a spot on the lung”. Hamartomas are the most common type of benign (not harmful) lung tumor. About 8% of all lung tumors are hamartomas. Most are found in the outer part of the lung, but some are found in the bronchial tubes. Other benign tumors are bronchial adenomas and papillomas. These tumors generally cause no problems but should be monitored regularly by healthcare professionals for any changes.
If you have cancer that has metastasized from another primary organ, it won't be classed as lung cancer.
Lung cancer staging helps you and your medical team understand where the cancer is located, and if it has spread. Staging helps when deciding on an effective treatment plan. It is done at initial diagnosis and re-assessed during treatment.
The TNM staging system for non-small cell lung cancer
TNM stands for tumor, node and metastasis.
Tumor – this assesses the size of the primary tumor and its growth pattern
Node – this checks if the cancer is affecting lymph nodes
Metastasis – checks whether distant organs are being affected.
The results of the TNM assessment determine the stage of the lung cancer. The stages go from zero to four. Stages I through IV are in Roman numerals and have further A and B sub-divisions.
The malignant cancer is in situ and has not moved from where it originated.
The cancer is in one lung only. It's not in the lymph nodes and has not metastasized. Stages IA and IB grade the size of the tumor and how it is behaving.
The cancer is in the lung where it began. It hasn't metastasized to distant organs in the body. Stages IIA and IIB grade the size of the tumor and what areas it is affecting.
The cancer is described as locally advanced. It has spread in the chest area but is not in other parts of the body. This stage has three levels, A, B and C, which chart the cancer’s severity and spread.
Stage IV tumors have metastasized to distant organs of the body. The tumors are of any size and may have spread to lymph nodes. This stage is also divided into A and B to grade the severity of the cancer's advance.
Staging for small cell lung cancer
The TNM staging used for non-small cell lung cancer may also be used for SCLCs but it is not so critical to do this for SCLCs.
The two-stage system for SCLCs is divided into a limited stage and an extensive stage.
If you are at a limited stage, you may be offered chemotherapy and radiation therapy to try to eliminate the cancer.
The cancer will probably only be in one lung which means that treatment can be directed towards one site. Only one in three people diagnosed with SCLC will be at a limited stage.
If you are in the extensive stage, this means that the cancer has spread throughout the lung, possibly to the other lung, and to lymph nodes or other parts of the body.
Treatment for people in the extensive stage is aimed at controlling, not eliminating, the cancer and is likely to be a course of chemotherapy.
Lung cancer can be difficult to detect early. This is because tumors can grow undetected in the lungs without causing any discomfort.
Common symptoms are:
A persistent or worsening cough
Feeling out of breath
Pain in the chest area
A hoarse voice
Recurrent bouts of bronchitis or pneumonia
Blood in the sputum
Other symptoms that lead to diagnosis may involve other areas of the body, and often indicate that the lung cancer has spread. These include loss of weight, headaches, blood clots, or fractures.
An initial diagnosis is sometimes made because of a concern about symptoms, or because of a history that indicates risk may be high.
Chest x-rays and blood tests are followed by a CT scan or a PET scan. This gives a more precise picture of where the cancer is and if it has spread.
You will need to have tests on the cells and fluid from inside and around the lung to make sure you really have lung cancer and what type it is. There is a range of different tests that use biopsies and ultrasound. Common procedures are a bronchoscopy (insertion of a tube into the lung) and an endobronchial ultrasound scan (EBUS). You may need a local or general anesthetic for some of these tests.
Once the tests have been completed, a diagnosis can be made together with an assessment of the stage the lung cancer has reached. Understanding your condition can help you be more knowledgeable.
Treatment for lung cancer will depend on:
The type of lung cancer that has been diagnosed
Where it is situated
The patient's general health
Chemotherapy is often the main treatment for lung cancer although it is often combined with other treatments. Similarly, the drugs given in chemotherapy can be adjusted for effectiveness.
Chemotherapy can be given at any part of the treatment process: to shrink tumors, before or after surgery, to alleviate symptoms, and combined with radiation therapy.
Typically, you will undergo a course of four-six chemotherapy cycles over six months. You'll then have more tests to assess how your body is responding so that the right treatment can proceed.
If you have non-small-cell lung cancer that's only in one lung, surgery to remove the cancerous cells can be effective. This is often followed by a course of chemotherapy.
There are three types of surgery for lung cancer:
A wedge resection or segmentectomy removes a small piece of the lung
A lobectomy removes a large part of the lung
A pneumonectomy removes the entire lung
Many types of radiation therapy are used to kill cancer cells or shrink tumors. Most radiation is applied externally, but some can be applied internally through an implant.
Palliative radiotherapy may be used to alleviate symptoms when the lung cancer is in an advanced stage.
Patients with small-cell lung cancer may have radiation to the brain. It is common for SCLC to spread to the brain, so prophylactic cranial irradiation is often a part of the treatment plan.
Targeted therapy is where lung cancer treatments target specific aspects found in the tumor’s DNA. It's done by molecular or biomarker testing. This approach can have fewer side effects. It focuses on specific aspects of the cancer cells and spares the normal, healthy cells from destructive treatments. Targeted therapy is not possible for every lung cancer patient.
The National Cancer Institute statistics³ for life expectancy in lung cancer patients measure the number of people who survive after five years. For all types of lung cancer, the five-year survival rate is 21%. It’s a little lower for men (17%) and a little higher for women (24%). The five-year survival rate for NSCLC is 25% and just 7% for SCLC.
Out of all cancer deaths, lung cancer is the highest⁴. However, better survival and cure rates are possible with early detection, and effective treatment options are always improving. Also, as more people stop smoking, the number of new cases is dropping.
Lung Adenocarcinoma (2021)
Cancer Stat Facts: Lung and Bronchus Cancer | Surveillance, Epidemiology, and End Results Program (SEER)
Key Statistics for Lung Cancer | American Cancer Society