Types of Lung Cancer

There are two main types of lung cancer: small cell and non-small cell lung cancer (NSCLC). Non-small cell lung cancer, the more common and slow-growing of the two, consists of different subtypes, mainly lung adenocarcinoma, large cell lung carcinoma, and squamous cell carcinoma of the lungs. Small cell lung cancer, which is less common and more aggressive, is further broken down into two subtypes, small cell carcinoma and combined small cell carcinoma.

Prognosis and treatment will look different depending on the specific type of lung cancer. Understanding the characteristics of each type of lung cancer can empower those with lung cancer to make the best treatment decisions.

Woman with Cancer Visits the Doctor

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Non-Small Cell Lung Cancer

Non-small cell lung cancer is the most common type of lung cancer, making up 80% to 85% of all lung cancers. Subtypes of NSCLC, which start from different types of lung cells, are grouped together as NSCLC because their treatment and outlooks are often similar. NSCLC often develops slowly and causes few or no symptoms until it has advanced. 

Smoking is the main risk factor for NSCLC, accounting for around 90% of cases. The exact risk depends on the number of cigarettes someone smokes each day and for how long they have smoked. Secondhand smoke also raises the risk of lung cancer. It's important to note that some people who never smoked can also develop lung cancer.

Radon exposure and exposure to air pollution or water with a high level of arsenic may also increase one's risk of lung cancer as well. Radon gas breaks down into tiny radioactive particles that can deposit themselves into the lungs. The first recorded instance of radon exposure's adverse impact on the lungs was in 1556 when researchers found radon was destroying the lungs of miners in Germany. Today, exposure to radon remains a leading cause of lung cancer.

The five-year survival rate (how many people are alive five years after their diagnosis) for NSCLC is estimated to be 26.3%. Many factors, such as age and concurrent conditions, can impact survival rates. This number does not reflect recent advancements in treatment. To better understand your individual prognosis, it is more important to examine personal factors such as genetics, lifestyle, and family history.

What Are Lung Nodules?

A lung nodule, also called a pulmonary nodule, is a small round or oval-shaped growth in the lung. Lung nodules are not all malignant or cancerous; the majority of them that show up on your CT scan are benign. They are typically smaller than around 1.2 inches in diameter. If the growth is larger than that, it is called a pulmonary mass and is more likely to represent a cancer than a nodule. Risk factors for malignant pulmonary nodules include a history of smoking and older age.

If a lung nodule is found on your CT, one common approach is to get a repeat CT scan to see if the nodule is growing over time, from a few months to a year, depending on how likely your doctor thinks that the nodule could be cancer. This is based on the size, shape, and location of the nodule, as well as whether it appears to be solid or filled with fluid. If a repeat scan shows that the nodule has grown, your doctor might also want to get another imaging test called a positron emission tomography (PET) scan, which can often help tell if it is cancer. If a nodule is large enough and suspicious, biopsy or resection may be immediately pursued.

Adenocarcinoma

Adenocarcinoma is the most common form of non-small cell lung cancer, accounting for 30% of all cases overall and about 40% of all non-small cell lung cancers. It begins in the epithelial cells of the lung.

This type of lung cancer occurs mainly in current or former smokers, but it is also the most common type of lung cancer seen in non-smokers. It is more common in women than in men, and it is more likely to occur in younger people than other types of lung cancer. Adenocarcinoma is more likely to be found before it has spread.

Survival rates vary by the stage of the lung cancer. The five-year survival rate is low, estimated at less than 12% to 15%. For those with stage 1 adenocarcinoma, the five-year survival is estimated between 70% to 85%, but when cancer has metastasized, the five-year survival rate drops to less than 5%.

People with a type of adenocarcinoma called adenocarcinoma in situ tend to have a better prognosis than those with other types of lung cancer.

Squamous Cell Carcinoma

Squamous cell carcinoma (SqCC) develops in the squamous cells, which line the airways. SqCC is often found near the bronchi. Of the 80 to 85% of lung cancers that are non-small cell, it is estimated that 30% of these cancers are SqCC. 

This type of lung cancer is often linked to a history of smoking. About 90% of SqCC cases are caused by tobacco smoking.

Squamous cell lung cancer is usually diagnosed after the disease has spread. The average five-year survival rate is 24%. The survival rate is significantly higher if the disease is detected and treated early.

Adenosquamous Carcinoma

Adenosquamous carcinoma of the lung has characteristics of adenocarcinoma and squamous cell lung cancer. It is a rare subtype of non-small cell lung cancer, making up 0.4% to 4% of cases.

Large Cell Undifferentiated Carcinoma

Large cell undifferentiated carcinoma, also known as large cell lung carcinoma (LCLC), tends to be faster-growing than other lung cancers, but it is less common than both squamous cell carcinoma and adenocarcinoma of the lungs. LCLC accounts for 10% to 15% of all NSCLC cases, and can be found in any part of the lung.

As with other types of lung cancer, risk factors include smoking and exposure to secondhand smoke. Additionally, exposure to radon is thought to be a risk factor for LCLC.

In large cell neuroendocrine carcinoma, a subtype of large cell lung carcinoma, certain gene mutations RUNX1 and ERBB4, can appear in the cancer itself. It tends to grow and spread quickly and is very similar to small cell lung cancer. It is diagnosed after a cytology description shows a lack of squamous, glandular, or small cell (neuroendocrine) differentiation.

The prognosis is often worse for LCLC than other lung cancers. Possibly due to the development of tumors at the lungs' periphery, classic signs associated with lung cancer, such as coughing, often do not appear until later. The diagnosis can therefore be delayed, which worsens the prognosis. Newer immunotherapies have shown to be a promising area of development in treating LCLC.

Other Subtypes of NSCLC

Other subtypes of NSCLC include adenosquamous carcinoma and sarcomatoid carcinoma, which are much less common.

Adenosquamous carcinoma meets the criteria for both SqCC and adenocarcinoma. A study showed that patients with adenosquamous carcinoma generally have a better prognosis than those with squamous cell carcinoma.

Sarcomatoid carcinomas are very rare but aggressive, and are estimated to account for less than 3% of all non-small cell lung cancers. It looks like a mixture of carcinoma and sarcoma. The five-year survival rate is about 20%. Additional research into the molecular profiling of tumors has been suggested to improve therapies.

Small Cell Lung Cancer 

Small cell lung cancer (SCLC) is less common than non-small cell lung cancer, and is estimated to comprise roughly 10% to 15% of lung cancers. SCLC often starts in the bronchi, or the airways that lead from the trachea into the lungs and then branch off into progressively smaller structures. SCLC quickly grows and spread to other parts of the body, including the lymph nodes.

Exposure to a carcinogen, such as tobacco smoke or certain environmental toxins like asbestos, can cause modifications to the body's DNA. Sometimes oncogenes, or genes that suppress tumor activity, can be damaged, making the body vulnerable to developing cellular malignancy. Older age and compromised immune systems can also increase vulnerability to the disease.

About 70% of people with SCLC will have cancer that has already spread at the time they are diagnosed. Since this cancer grows quickly, it tends to respond well to chemotherapy and radiation therapy.

Cancer and Genes

DNA is your body's recipe for proteins. When the DNA is damaged, it can't always make proteins correctly. Oncogenes are genes that can cause cancer. Proto-oncogenes have the potential to become oncogenes when they are subject to small modifications. This can occur through mutation and is a process regulated by small RNAs.

The general five-year survival rate for people with SCLC is 6%. For people with localized SCLC, which means the cancer has not spread outside of the lung, the overall five-year survival rate is 27%.

Small Cell Carcinoma

Small cell carcinoma, also known as oat cell cancer, is classified as a neuroendocrine disease because it develops in cells that act both like nerve and hormone cells. Small cell carcinoma is the most common type of SCLC, and looks flat under a microscope, like oats. 

Combined Small Cell Carcinoma

Combined small-cell lung carcinoma (C-SCLC) comprises 30% of SCLC cases. It is classified as small cell carcinoma with the characteristics of non-small cell lung carcinoma.

The median age of C-SCLC patients is between 59 and 64 years old. Epigenetic modifications, or changes to gene expression due to environmental exposure, are thought to play a significant role in the development of C-SCLC. Inherited risk is thought to be less important, and more emphasis is put on behavioral and environmental factors.

Mesothelioma

Mesothelioma is a rare but aggressive cancer of the chest lining, with about 3,000 cases being diagnosed each year in the United States. It develops in the thin layer of tissue that covers most of the internal organs called the mesothelium. The most common form, called pleural mesothelioma, occurs in the lining of the lungs. 

Mesotheliomas are much more common in older people than younger people. The average age at the time of diagnosis is 72.

Eight out of 10 people with mesothelioma report asbestos exposure, which is why it is considered the biggest risk factor for developing the disease. When asbestos fibers are inhaled, they can travel into the smallest airways and irritate the lung lining, or pleura. This irritation results in inflammation and damage that can eventually lead to the creation of abnormal cancer cells. 

Other risk factors include radiation therapy, age, and genetics. Radiation pertains particularly to those who have received high doses of radiation therapy to the chest, such as people with lymphoma. About 1% of people diagnosed with mesothelioma have inherited a genetic mutation from a parent that has put them at increased risk of this disease.

Cancers That Commonly Spread to the Lungs

Common tumors that metastasize to the lungs include:

  • Breast cancer
  • Colon cancer
  • Prostate cancer
  • Sarcoma,
  • Bladder cancer
  • Neuroblastoma
  • Wilm's tumor

It's important to note that almost any cancer has the capacity to spread to the lungs.

Other Rare Lung Cancers

Lung Carcinoid Tumors

Less than 5% of lung tumors are lung carcinoid tumors. Of these, nine of 10 are typical, and they are usually slow-growing. Out of every 10, there is one atypical, which is faster-growing. Lung carcinoid tumors occur in the neuroendocrine cells. Depending on where they are located in the lung, they may be referred to as central or peripheral carcinoids.

Chest Wall Tumors

The chest wall protects the lungs, and comprises many parts, including skin, fat, muscle, tissue, and lymphatic vessels. Chest wall tumors are classified as either primary or secondary. Primary tumors are those located in muscle, fat, blood vessel, nerve sheath, cartilage, or bone. Secondary chest wall tumors are less straightforward. For example, they can be a result of breast carcinoma that has grown beyond the site of origin.

Mediastinal Tumors

The mediastinum separates your lungs from the rest of your chest. This body cavity contains your heart, aorta, esophagus, thymus, and trachea. There are several kinds of mediastinal tumors, but they are rare. However, unlike most other cancers, they are usually diagnosed in young to middle-aged adults, most commonly between 30 and 50 years old.

A Word From Verywell

Being diagnosed or having risk factors for lung cancer can be scary and overwhelming. People live well even with cancer. It is never too late to reduce your risk of lung cancer, which can be done by talking to your support network about smoking cessation. Reducing environmental risk to second-hand smoke or toxins such as asbestos can also help reduce your risk burden, especially if you also smoke.

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