Primary and Secondary Lung Cancer

Lung cancer is described based on where the disease originated. Cancer that starts in the lungs and is unrelated to any previous cancer is called primary lung cancer. Secondary lung cancer, on the other hand, is cancer that spreads to the lungs from another part of the body.

A second primary lung cancer is a new lung cancer that develops in the lungs unrelated to the original cancer. There is also is a type of lung cancer referred to as lung cancer of unknown origin.

This article looks at the different types of lung cancer, their causes, symptoms, and how you can treat and manage each type.

Primary Lung Cancer

Primary lung cancer is cancer that begins in the lungs and is most often simply referred to as "lung cancer." Your healthcare provider probably won't use the word "primary" to describe it.

Non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), carcinoid tumor, and other rarer types of lung tumors are all primary lung cancers.

Common causes for primary lung cancer include:

• Smoking
• Exposure to radon
• Asbestos exposure
• Secondhand smoke
• Air pollution

Symptoms vary, depending on the type and stage of lung cancer. General cancer-related symptoms including fatigue, unexplained weight loss, and decreased appetite are common.

Symptoms of primary lung cancer can also include:

• A persistent cough
• Hemoptysis (coughing up blood or bloody mucous)
• Pain in the chest, shoulder, and back
• Shortness of breath

Complications can include hypoxemia (low blood oxygen level) or pleural effusion (fluid in the space around lungs), which can manifest with shortness of breath.

When Primary Lung Cancer Spreads

Cells from a primary lung cancer tumor can sometimes break off and travel through the bloodstream or the lymphatic system. These cells can settle in other organs or regions of the body and begin to grow new tumors. This process is called metastasis.

The tumors that grow in these new areas are composed of lung cancer cells, so they're still referred to as lung cancer. Specifically, they are referred to as “primary lung cancer metastatic to [area where they have spread to].”

For example, if lung cancer has spread to the brain, it would be referred to as “primary lung cancer metastatic to the brain,” not “brain cancer.” It may also be referred to as "lung cancer metastatic to the brain” or “metastatic brain cancer from the lung.” Lung cancer in the brain is considered secondary brain cancer.

The most common sites for lung cancer metastases are:

• Lymph nodes
• Liver
• Bones
• Brain
• Adrenal glands

Lung cancer may be diagnosed after it has already spread to other areas of the body. In 40% of people newly diagnosed with lung cancer, tumors have already metastasized elsewhere.

Treatment for Metastasized Lung Cancer

Treatment for cancers that originated from lung cancer tumors depends upon where the cells have metastasized to.

Secondary Lung Cancer

In the same way that a brain tumor that originates from a primary lung tumor is deemed secondary brain cancer, a tumor in the lungs that has metastasized from cancer elsewhere in the body is called secondary lung cancer.

Cancer that originates in the breast and spreads to the lungs, for instance, falls into this category. A healthcare provider will likely use designations such as primary breast cancer metastatic to the lung, breast cancer metastatic to the lung, or metastatic lung cancer from the breast.

Here, cancerous breast cells, rather than cancerous lung cells, are what form the lung tumor. The same follows for secondary lung cancer due to metastatic liver cancer or pancreatic cancer.

Symptoms of secondary lung cancer are the same as the symptoms of primary lung cancer.

Treatment of Secondary Lung Cancer

Secondary lung cancer may require different treatment approaches than primary lung cancer. Chemotherapy is often the first course of treatment for cancer metastatic to the lung.

Other treatment options may be used, depending on the primary cancer. Options may include targeted therapies, immunotherapy, or a combination of treatments.

Palliative therapy may be used to reduce pain or help manage other symptoms. It can extend survival and improve your quality of life, but it is not offered as a cure.

In an effort to make treatment most effective, researchers have been studying the use of inhaled chemotherapy, which offers some hope of delivering the cancer-killing medication directly to the lungs.

Second Primary Lung Cancer

After being diagnosed with lung cancer once, another cancer can later develop in one of your lungs. This type of malignancy is known as "second primary lung cancer" because it appears after an earlier diagnosis and represents a new origin point.

Approximately 1 to 2% of lung cancer patients develop second primary lung cancer each year. A second primary lung cancer may be found at any time after your first diagnosis.

In some instances, this second primary lung cancer may be caused by the treatments you received for your original cancer.

Risks for Second Primary Lung Cancer

The greatest risk factor for a second primary lung cancer is continued smoking.

Some cancer treatments can also increase your chances of second primary cancers. Chemotherapy and radiation therapy each raise the risk of developing another cancer in a lung or anywhere in your body.

Other factors that impact your likelihood of second primary cancer include inherited gene mutations and exposure to carcinogens such as tobacco smoke.

Treatment for Second Primary Lung Cancer

Treatment options for a new lung tumor of a different origin are the same as the general treatments available for a first primary lung cancer. The recommended course depends on the type of cancer and what stage it has reached.

Two Primary Lung Cancers

Developing two separate, unrelated lung cancers simultaneously may seem very strange, but it's not uncommon. Actually, it is understandable when you consider that the risk factors for both primary tumors are the same.

For example, people who carry a genetic risk for breast cancer sometimes develop two separate and unrelated breast cancers due to a gene mutation they carry. Likewise, people who have a genetic risk for lung cancer or are exposed to substances that cause the disease, such as tobacco, may also develop two unrelated lung cancers.

In this scenario, both tumors would be considered primary lung cancers. It can be difficult at first to know whether two cancers like this are related. Healthcare providers are increasingly making use of advanced testing such as molecular profiling of lung cancers to make these types of determinations.

Cancer of Unknown Primary Cause

Healthcare providers can’t always determine the origin of a lung cancer tumor. Tests may not be able to confirm if the cancer started in the lung or another part of the body. In this instance, the tumor is known as "cancer of unknown primary" or “metastatic cancer to the lungs of unknown origin."

The cells in these tumors are often very undifferentiated, meaning it's challenging to tell what type of cell they were before they became malignant—and, therefore it's hard to identify where they traveled from.

Treatment recommendations are usually influenced by how the cancer originated, so it's helpful to identify the primary cancer. However, even without that information, your healthcare provider may determine treatments which treatments would be best for you. 

A Word From Verywell

Primary and secondary lung tumors can produce the same symptoms. But the treatment and prognosis differ for different primary cancers. Your healthcare provider will work with you to determine the origin of your cancer and discuss all of your treatment options. When looking for information about your cancer, or seeking a support group, be sure to look for resources that correspond to your primary tumor, because this is where you will find the information that applies to your situation.