Primary and Secondary Lung Cancer

Aside from there being different types of lung cancer, there are different classifications that are based on where the disease originated. When cancer starts in the lungs and is unrelated to any previous cancer, it is referred to as primary lung cancer. Secondary lung cancer, on the other hand, is a disease that has spread to a lung from another part of the body.

Secondary 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.

possible causes of a lung mass
Illustration by Brianna Gilmartin, Verywell

Different factors can raise your risk of cancer spreading or developing new cancers, and treatment options sometimes vary depending on the type of cancer you have and whether it is primary or secondary.

These labels can be confusing, but it's important to understand all of their nuances so you can better understand your disease and make confident choices about next steps.

Primary Lung Cancer
  • Tumor originates in a lung

  • Cancerous cells are lung cells

Secondary Lung Cancer
  • Tumor originates elsewhere in the body

  • Cancerous cells are from the origin area (e.g., breast cells)

Primary Lung Cancer

A primary lung cancer is a cancer that begins in the lungs. Primary lung malignancy, or a primary tumor, is most often simply referred to as "lung cancer." Your doctor probably won't use the word "primary" if your case falls into this category.

Any type of lung cancer can be a primary lung cancer, including non-small cell lung cancer, small cell lung cancer, carcinoid tumor, or other rarer types.

Common causes for primary lung cancer include:

Symptoms vary depending on the type and stage of lung cancer. Common symptoms of primary lung cancer include:

General cancer-related symptoms including fatigue, unexplained weight loss, and decreased appetite are also common.

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 made 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 the 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.” The cancer in the brain is considered secondary brain cancer.

The most common sites for lung cancer metastases are:

Unfortunately, lung cancer is often not diagnosed until it has spread to other areas of the body. In 40% of those 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.

Treating Lung Cancer Metastases
Location First Choice Support
Lymph nodes

Surgery 

Adjuvant therapies, including radiationchemotherapy, and targeted therapy
Bone Pain medications, radiation therapy Medications to prevent the breakdown of bone
Brain Palliative treatments including steroids to reduce swelling, pain relief, and anti-seizure medications to control symptoms Radiation therapy for symptom relief
Liver

Chemotherapy

Surgery (if tumors are small and few); embolization 
Adrenal 
glands
Chemotherapy  Surgery (if only one spot is present) 

Secondary Lung Cancer

In the same way that a brain tumor that originates from a primary tumor in the lungs is deemed secondary brain cancer, a tumor in the lungs that occurs because of metastasis of cancer somewhere else 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 doctor will likely use familiar labels 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 brain cancer (malignant brain cells), pancreatic cancer (malignant pancreatic cells), and so on.

Cancer first appears in one lung. Technically speaking, if the cancer spreads to the other lung, the new tumor is considered a secondary lung cancer. It will be referred to as a lung metastasis from the primary lung cancer. On your lab report, it might say something like“primary lung cancer metastatic to another region in the lungs.”

Often, there are no symptoms specific to secondary lung cancer. If symptoms are present, they're usually similar to 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. 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.

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

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

Second Primary Lung Cancer

After being diagnosed with lung cancer once, a new cancer can later develop in one of your lungs that is completely unrelated to the first tumor. It may be the same type of lung cancer but differ from the first in its molecular characteristics. That is, this second primary lung cancer would have started with a different cluster of cancer cells than the first tumor.

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 shortly after your first diagnosis or years later.

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 is continued smoking. Unfortunately, some cancer treatments can also increase your chances of second primary cancers. Specifically, having undergone chemotherapy or radiation therapy raises the risk of developing a new 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 different origin are the same as the general treatments available for lung cancer. The recommended course depends on whether it is non-small cell or small cell lung cancer and what stage the cancer has reached.

Even if all tumors have been surgically removed and your primary cancer is in remission, cancer can recur years later. If the recurrent cancer is the same type of cancer (lung cancer cells with the same mutation), the new appearance will be considered a metastasis from the primary lung cancer, not a new primary or second primary cancer.

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. Doctors 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

Doctors 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, 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 doctor should still be able to determine treatments that can be successful. 

A Word From Verywell

There are many challenging terms in oncology, and most people are completely unfamiliar with the jargon before their diagnosis. Don't let clinical language intimidate you. Ask a lot of questions and, if the answers aren't clear, ask again. Being informed about your specific type of cancer and all of your options can sometimes make a huge difference in the outcome of your disease.

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