There is a difference between cancer that originates in the lungs and cancer that travels to your lungs. You may hear some medical professionals call both lung metastases, which can be confusing.
It’s important to know that metastatic lung cancer originates in the lungs but spreads to other parts of the body. No matter which part of the body those cancer cells migrate to, the cancer is still called lung cancer.
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About 85% of all lung cancer is non-small cell lung cancer (NSCLC). Adenocarcinoma, squamous cell, and large cell carcinomas are the main types of NSCLC. The remaining 15% of lung cancers are small-cell lung cancer (SCLC).¹
Both non-small cell and small cell lung cancer may not cause any symptoms until the lung cancer has spread.
Risk factors for lung cancer
Smoking continues to account for 85% of all lung cancer diagnoses.² Also, if you have quit smoking or get exposed to secondhand smoke, you can still develop lung cancer. According to Johns Hopkins University, smoking and exposure cause nearly half a million deaths a year, making it the number one risk factor for lung and associated cancers.
Other risk factors include:
Being age 65 or older (male or female)
Genetics or family history of lung cancer
Exposure to environmental exposure to pollutants such as radon, fuel exhaust, or asbestos
Cancer is caused by abnormal cell growth. First, cells multiply, and the formation of tumors begins. Sometimes cancer cells break off from the original tumor and travel through the bloodstream or lymphatic system to other organs. There it sets up residence and may begin to grow into another tumor, also called a lesion.
Pathologists examine newly discovered cancer cells under a microscope. If they match the original lung cancer cells, the cancer is said to have metastasized from your lungs.
If cells are found in your lungs that originated from another type of cancer, such as breast cancer, they would call it breast cancer metastasis to your lungs. They take the name from the originating cancer site.
What symptoms would alert you to the possibility that you have metastatic lung cancer? It can be difficult as you may or may not present any particular symptoms until cancer has advanced into metastasis (usually called stage IV⁵ cancer). In addition, your symptoms will depend on which organ cancer has spread to.
You may experience³:
A persistent cough
Shortness of breath
Unexplained weight loss
Blood clots in your legs or lungs
Pain in the bones
Headache and other neurological symptoms
Every person is different, and every lung cancer diagnosis is unique. You may not have every symptom. You may have symptoms that come and go. Once your lung cancer has spread, symptoms tend to surface or worsen depending on your specific condition at the time of metastasis.
Often your initial lung cancer is discovered by accident through routine imaging and blood tests. Imaging tests include X-rays, CT or PET scans, or MRIs.
A biopsy (taking a tissue sample) is often taken by putting a thin telescope into the windpipe to look into the lungs, making an incision through which a telescope is placed, or by a thin needle that extracts cells. A pathologist then reviews the tissue to determine your diagnosis.
Forming a diagnosis
To diagnose lung cancer and determine whether it has metastasized, your doctor may use a combination of health history, physical examination, lab tests, and imaging. A critical area of experimental research is the use of blood tests to screen for cancer.⁴
Metastatic lung cancer may be localized, regional, or distant.
Local metastasis means that the cancer cells have spread to other parts of your lung.
Regional metastasis means that cancer cells have spread to nearby lymph nodes, organs, or other tissue.
Distant metastasis means that cancer cells have spread to remote parts of your body.
Common metastatic sites include the adrenal glands (located above the kidneys), the bones, the brain, liver, skin, or the other lung.
Staging is the part of the diagnostic process which tells you if cancer has spread, what treatment options exist, and the prognosis. The earlier the stage, typically, the more the likelihood of remission or becoming cancer-free.
Your physician will use what’s called the TNM factor system to classify your cancer into one of the following stages by determining:
Tumor size and location
Node involvement (regional lymph nodes)
Metastasis (has it occurred)
There are four stages of non-small cell lung cancer.
Stage 0 refers to abnormal cells detected in the lining of the respiratory tract with no further spread.
Abnormal cells have merged into a cancerous lesion and have not spread to lymph nodes. In some cases, cancer has moved to the airway connecting the trachea to the lung (bronchus) but not to the trachea's ridge (carina), which divides the left and the right main bronchi.
Tumors have grown from 4cm to 5cm and may or may not have reached local lymph nodes. Therefore, stage II is divided into stage IIA or IIB.
This stage is further broken down into IIIA, IIIB, or IIIC, depending on size, location, and metastasis. It is common for stage III cancer to spread to the lymph nodes located between the lungs or the lymph nodes in the other lung.
Stage IV is when advanced lung cancer has spread regionally or distantly throughout the body.
Small cell lung cancer gets categorized as either limited-stage or extensive-stage. The limited stage is similar to NSCLC stage III and the extensive stage to stage IV.
Treatment varies, depending on what stage cancer is in and the condition of the patient. For example, at stage IV, metastatic lung cancer is usually best treated by chemotherapy, immunotherapy or targeted therapy.
According to the National Cancer Institute, other treatment options may include:
Surgery (in select patients)
Endoscopic stent placement
Treatment side effects
Treating metastatic lung cancer has side effects. Chemotherapy, for instance, commonly causes hair loss, weight changes, fatigue, nausea, vomiting, diarrhea, constipation, or mouth sores (mucositis). There is also an increased risk of infection from bone marrow suppression as white blood cell count decreases.
However, these side effects usually lessen or go away after treatment is completed.
Research is constantly looking at new metastatic lung cancer therapies. Patients can pre-screen for inclusion in clinical trials and opt-in for experimental treatments.
On average, patients with stage IV lung cancer live for about two years. An interdisciplinary care team will typically help plan treatment that focuses on stopping or slowing the metastatic spread of cancer, improving and prolonging quality of life for as long as possible.
When metastatic lung cancer treatment options are exhausted, the focus is alleviating symptoms and supporting quality of life. Entering palliative care attends to pain control, sleep, and emotional and spiritual needs, including support for their family members.
Possibility of remission
Metastatic lung cancer can enter remission or not worsen for a few years. No one can predict whether or not cancer will recur after remission. However, advanced-stage metastatic lung cancer makes it more likely that cancer will return. It is treatable, but not usually curable.
Stage IV is the most advanced form of lung cancer. Estimated survival rates come from studying people with the same stage of cancer. However, they are still estimates.
According to Cancer Treatment Centers of America, people with metastatic single-cell lung cancer have a relative survival rate of 3% (over five years).⁵ That rate does not account for the exact care or type of treatment the individual is receiving. Similarly, these rates do not reflect newly available or experimental treatment options.
Understanding Lung Cancer | Oregon Health and Science University: Knight Cancer Institute
Former Smokers: What’s Your Risk for Lung Cancer? | Johns Hopkins Medicine
Lung Metastases (Metastatic Cancer) | UCLA Health
Study Examines Whether Blood Test Can Identify Early Cancers | NIH: National Cancer Institute
What is stage 4 lung cancer? | Cancer Treatment Centers of America