Lung cancer also has a preferred path of spread, traveling most often to the bones, brain, adrenal glands, and liver.

Why Does Lung Cancer Spread So Easily?

Lung cancer may metastasize readily because the lungs are a cellular traffic hub of the body. “The job of the airway is to deliver oxygen to all of your cells, so it’s easy for cancer cells to get from the airway lining to the blood and spread to other organs,” says Paul Bunn, MD, professor of medical oncology at the University of Colorado School of Medicine in Denver.

Why Do Lung Cancer Cells Spread to Certain Organs?

“Some organs produce a cellular signal that draws a particular cancer into it,” says Douglas Arenberg, MD, professor of pulmonary and critical care medicine at the University of Michigan Medical School in Ann Arbor. That’s where lung metastases are usually found. Scientists sometimes refer to it as the “seed and soil” hypothesis, the tumor being the seed and the soil being receptive to that seed. Cancer is always named after the place in the body where it started. That means if lung cancer spreads to the brain, it’s called “metastatic lung cancer,” not “brain cancer.”

Breaking Down the Common Areas Lung Cancer Spreads

While lung cancer can spread to many areas of the body, certain places are more common.

Bones

Between 30 percent and 40 percent of people who have the most common type of lung cancer develop bone metastases at some point. Lung cancer that spreads to the bones typically affects the spine, ribs, pelvis, and long bones in the body, though it can spread to any bone in the body. The spread may be seen on imaging, but often isn’t diagnosed until it causes pain or other problems. Tests such as a bone scan, CT scan, X-ray, PET scan, or MRI can detect cancer that’s moved to the bones.

Brain

Studies show between 16 percent and 20 percent of people with lung cancer will develop brain metastases. The risk is even higher for those with certain types of tumor mutations. Symptoms of brain metastases may include headaches, loss of balance, seizures, difficulty talking, vision changes, memory problems, and fatigue. Doctors can spot lung cancer that’s spread to the brain by performing a CT scan or an MRI.

Adrenal glands

The adrenal glands (small glands that sit on top of the kidneys) are a common site for lung cancer metastasis. Usually, cancer that spreads to the adrenal glands doesn’t cause symptoms. However, in rare cases, it may trigger back or abdominal pain. Doctors can perform various scans to see if cancer has traveled to the adrenal glands.

Liver

Most lung tumors that spread to the liver invade other sites at the same time. Lung cancer that moves to the liver may not cause symptoms. When it does, symptoms may include loss of appetite, nausea, fever, pain in the upper right side of the abdomen, weight loss, sweats, and jaundice (yellowing of the skin or whites of the eyes). Doctors can perform tests, such as an abdominal ultrasound, CT scan, or PET scan to look for cancer that’s spread to the liver.

Other areas

Occasionally, lung cancer can spread to other areas of the body, including the pancreas, stomach, small and large intestines, skin, eyes, kidneys, and breasts.

Does Size Matter?

There’s a misconception that cancer must reach a certain size before it’s capable of spreading, but there’s no given size threshold that allows a cancer to metastasize, says Dr. Arenberg. Some cancers metastasize before they’re detectable. That said, larger tumors do tend to be more likely to find their way elsewhere. “One way to look at a tumor is that every day, it’s sort of playing the lottery,” Arenberg says. “The more cells there are, the more likely it is that a few will win the lottery and gain the ability to invade the bloodstream or lymph system,” he explains. That’s why early detection is often key to better odds of survival.

Can Metastasis Be Detected Before Symptoms Appear?

A number of tests, including blood tests, CT scans, bone scans, and MRIs, can be performed to look for metastases. The specific tests done will depend on your symptoms. The generally accepted course, says Arenberg, is to mention any symptoms to your doctor and then treat the metastases to control those problems and improve your quality of life.

What Should You Look For?

Tell your doctor if you have any symptoms that are out of the ordinary, especially those that could indicate metastasis, such as:

Any kind of new painNeurological symptoms such as weakness or changes in your ability to walk or grip things or a new headacheUnintentional weight loss or loss of appetiteFatigue or weaknessJaundice