Doctors use many tests to diagnose cancer and find out if it has spread from the lung. Some tests may also determine which treatments may be the most effective. A biopsy is the only way to make a definitive diagnosis of lung cancer. Imaging tests may be used to find out whether the cancer has metastasized, but they can never be used alone to diagnose lung cancer. Your doctor may consider these factors when choosing a diagnostic test:

• Size, location, and type of cancer suspected
• Age and medical condition
• Severity of symptoms
• Previous test results

In addition to a physical examination, the following tests may be used to diagnose and stage [2] lung cancer:

Biopsy [3]. A biopsy is the removal of a small amount of tissue for examination under a microscope. In recent years, doctors have learned it is helpful to have a larger tumor sample in order to determine the subtype of NSCLC and to do additional molecular testing (see below). If not enough of the tumor is removed to do these tests, another biopsy may be needed. The sample removed from the biopsy is analyzed by a pathologist (a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease). If cancer cells are found, the pathologist will determine if it is small cell lung cancer or NSCLC, based on what it looks like when seen through a microscope.

Common procedures doctors use to collect tissue for the diagnosis and staging [2] of lung cancer are listed below:

Sputum cytology. If lung cancer is suspected, the doctor may ask a person to cough up some phlegm so it can be looked at under a microscope. A pathologist can find cancer cells mixed in with the mucus. However, sputum cytology provides a smaller amount of tissue than is needed to completely diagnose lung cancer and perform molecular testing (see below).

Bronchoscopy [4]. In this procedure, the doctor passes a thin, flexible tube with a light on the end into the mouth or nose, down through the main windpipe, and into the breathing passages of the lungs. A surgeon or a pulmonologist (a medical doctor who specializes in the diagnosis and treatment of lung disease) may perform this procedure. The tube lets the doctor see inside the lungs. Tiny tools inside the tube can take samples of fluid or tissue so the pathologist can examine them. Patients are given mild anesthesia (medication to block the awareness of pain) during a bronchoscopy.

Needle aspiration/core biopsy. After numbing the skin, a special type of radiologist, called an interventional radiologist, removes a sample of the lung tumor for testing. This can be done with a smaller needle (to take a smaller sample) or a larger needle (called a core biopsy, to take a larger sample). The doctor uses the needle to aspirate (suck out) a small sample of tissue for testing. Often, the radiologist uses a chest CT scan or special x-ray machine called a fluoroscope to guide the needle. In general, a core biopsy provides more tissue than a needle aspiration, which is needed for diagnosis and molecular testing (see below).

Thoracentesis. After numbing the skin on the chest, a needle is inserted through the chest wall and into the space between the lung and the wall of the chest where fluid can collect. The fluid is removed and checked for cancer cells by the pathologist.

Thoracotomy. This procedure is performed in an operating room, and the patient receives general anesthesia. A surgeon then makes an incision in the chest, examines the lung directly, and takes tissue samples for testing. A thoracotomy is the procedure surgeons most often use to completely remove a lung tumor.

Thoracoscopy. Through a small cut in the skin of the chest wall, a surgeon can insert a special instrument and a small video camera to assist in the examination of the inside of the chest. Patients require general anesthesia, but recovery time may be shorter with a thoracoscopy given the smaller incisions. This procedure may be referred to as VATS (video-assisted thoracoscopic surgery).

Mediastinoscopy. A surgeon examines and takes a sample of the lymph nodes in the center of the chest (underneath the breastbone) by making a small incision at the top of the breastbone. This procedure also requires general anesthesia and is done in an operating room.

Bone marrow biopsy and aspiration [5]. This is a test used occasionally for small-cell lung cancer. Bone marrow has both a solid and a liquid part. A bone marrow biopsy is the removal of a small amount of solid tissue using a needle. An aspiration removes a sample of fluid with a needle. The sample(s) are then analyzed by a pathologist. A common site for a bone marrow biopsy and aspiration is the pelvic bone, which is located in the lower back by the hip. The skin in that area is usually numbed with medication beforehand, and other types of anesthesia may be used. 

Molecular testing of the tumor. Your doctor may recommend running laboratory tests on a tumor sample to identify specific genes, proteins, and other factors unique to the tumor. Results of these tests will help decide whether your treatment options include a type of treatment called targeted therapy (see Treatment [6]).

Imaging tests

In addition to biopsies and surgical procedures, imaging scans are vital to the care of people with lung cancer. However, no test is perfect, and no scan can diagnose lung cancer. Only a biopsy can do that. Chest x-ray and scan results must be combined with a person's medical history, a physical examination, blood tests, and information from the biopsy to form a complete story about where the cancer began and whether or where it has spread.

CT scan [7]. This test produces images that allow doctors to see the size and location of a lung tumor and/or lung cancer metastases. A CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors.

Positron emission tomography (PET) scan [8]. A PET scan is a way to create pictures of organs and tissues inside the body. A small amount of a radioactive substance is injected into a patient's body. This substance is absorbed mainly by organs and tissues that use the most energy. Because cancer tends to use energy actively, it absorbs more of the radioactive substance. A scanner then detects this substance to produce images of the inside of the body.

Magnetic resonance imaging (MRI) scan [9]. This test also produces images that allow doctors to see the size and location of a lung tumor and/or lung cancer metastases. An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. A contrast medium (a special dye) may be injected into a patient's vein to provide better detail. MRI scanning does not work well to take pictures of parts of the body that are moving, like your lungs, which move with each breath you take. For that reason, the MRI scan is rarely used to look at the lungs. However, it may be helpful to find lung cancer that has spread to the brain.

Scans are also available that use radioactive molecules, called tracers, injected into the blood to show where cancer is possibly located, such as:

Bone scan [10]. A bone scan uses a radioactive tracer to look at the inside of the bones. The tracer is injected into a patient's vein. It collects in areas of the bone and is detected by a special camera. Healthy bone appears gray to the camera, and areas of injury, such as those caused by cancer, appear dark.

PET scans have been replacing bone scans in the diagnosis of cancer and are often used in combination with information gathered from a CT scan, an MRI, an x-ray, and a physical examination.

Learn more about what to expect when having common tests, procedures, and scans [11].

After these diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is cancer, these results also help the doctor describe the cancer; this is called staging [2]. Learn more about the first steps to take after a diagnosis of cancer [12].

Finding out where the cancer started

Lung cancer starts in the lungs. Many other types of cancer start elsewhere in the body and spread to the lungs when they metastasize. For example, breast cancer that has spread to the lungs is still called breast cancer. Therefore, it is important for doctors to know if the cancer started in the lungs or elsewhere.

To find where the cancer started, the doctor takes into account the patient's symptoms and medical history, physical examination, the appearance of the tumor on x-rays and scans, and risk factors for cancer. A pathologist can perform tests on the biopsy sample to help find out where the cancer began, and the doctor may recommend other tests for the patient to rule out specific types of cancer. If, after these considerations, the doctor is still not sure where the cancer started, the doctor may give a diagnosis of metastatic cancer “of unknown primary.” Most treatments for metastatic cancer of unknown primary [13] that are first found in the chest are the same as those for metastatic lung cancer.

Stopping smoking

Even after lung cancer is diagnosed, it can still be beneficial to quit cigarette smoking. People who stop smoking have an easier time with all treatments, feel better, live longer, and have a lower risk of developing a second lung cancer. Stopping smoking is never easy and even harder when facing the diagnosis of lung cancer. People who smoke should seek help from family, friends, smoking cessation programs, and health care professionals. None of the smoking cessation aids available interfere with cancer treatment. Learn more about tobacco [14] and quitting smoking [15].