Lung Cancer (cont.)
How is lung cancer diagnosed?
Doctors use a wide range of diagnostic procedures and tests to diagnose lung
cancer. These include...
- The history and physical examination may reveal the presence of symptoms or signs that are
suspicious for lung cancer. In addition to asking about symptoms and risk
factors for cancer development such as smoking, doctors may detect signs of breathing
difficulties, airway obstruction, or infections in the lungs. Cyanosis, a
bluish color of the skin and the mucous membranes due to insufficient oxygen
in the blood, that suggests compromised function of the lung. Likewise, changes in
the tissue of the nail beds, known as clubbing, may also indicate lung
disease.
- The chest X-ray is the most
common first diagnostic step when any new symptoms of lung cancer are present.
The chest X-ray procedure often involves a view from the back to the front of
the chest as well as a view from the side. Like any X-ray procedure, chest
X-rays expose the patient briefly to a minimum amount of radiation. Chest X-rays may reveal suspicious areas in the lungs but are unable to determine if
these areas are cancerous. In particular, calcified nodules in the lungs or
benign tumors called hamartomas may be identified on a chest X-ray and mimic
lung cancer.
- CT (computerized axial tomography scan, or CAT scan) scans may be performed on
the chest, abdomen, and/or brain to examine for both metastatic and primary
tumor. A CT scan of the chest may be ordered when X-rays are do not show an
abnormality or do not
yield sufficient information about the extent or location of a tumor. CT scans
are X-ray procedures that combine multiple images with the aid of a computer to
generate cross-sectional views of the body. The images are taken by a large
donut-shaped X-ray machine at different angles around the body. One advantage of
CT scans is that they are more sensitive than standard chest X-rays in the
detection of lung nodules. Sometimes intravenous contrast material is given
prior to the procedure to help delineate the organs and their positions. A CT
scan exposes the patient to a minimal amount of radiation. The most common side
effect is an adverse reaction to intravenous contrast material that may have
been given prior to the procedure. There may be resulting itching, a rash, or
hives that generally disappear
rather quickly. Severe anaphylactic reactions (life-threatening allergic
reactions with breathing difficulties) to contrast material are rare. CT scans
of the abdomen may identify metastatic cancer in the liver or adrenal glands,
and CT scans of the head may be ordered to reveal the presence and extent of
metastatic cancer in the brain.
- A technique called a low-dose helical CT scan (or spiral CT scan) is
sometimes used in screening for lung cancers. This procedure requires a
special type of CT scanner and has been shown to be an effective tool for
the identification of small lung cancers in smokers and former smokers.
However, it has not yet been proven whether the use of this technique
actually saves lives or lowers the risk of death from lung cancer. The
heightened sensitivity of this method is actually one of the sources of its
drawbacks, since lung nodules requiring further evaluation will be seen in
approximately 20% of people with this technique. Of the nodules identified
by low-dose helical screening CTs, 90% are not cancerous but require up to two years of costly and often uncomfortable follow-up and testing. Trials are underway to further determine the utility of spiral CT scans in screening for lung cancer.
- Magnetic resonance imaging (MRI) scans may be
appropriate when precise detail about a tumor's location
is required. The MRI technique uses magnetism, radio waves, and a computer to
produce images of body structures. As with CT scanning, the patient is placed
on a moveable bed which is inserted into the MRI scanner. There are no known
side effects of MRI scanning, and there is no exposure to radiation. The image
and resolution produced by MRI is quite detailed and can detect tiny changes
of structures within the body. People with heart pacemakers, metal implants,
artificial heart valves, and other surgically implanted structures cannot be
scanned with an MRI because of the risk that the magnet may move the metal
parts of these structures.
- Positron emission tomography (PET) scanning is a specialized imaging technique
that uses short-lived radioactive drugs to produce three-dimensional
colored images of those substances in the tissues within the body. While CT scans
and MRI scans look at anatomical structures, PET scans measure metabolic
activity and functioning of tissue. PET scans can determine whether a tumor
tissue is actively growing and can aid in determining the type of cells within a
particular tumor. In PET scanning, the patient receives a short half-lived radioactive drug and receives approximately the amount of radiation exposure as two chest
X-rays. The drug discharges particles known as positrons from wherever they are taken up and used in the body. As the positrons encounter electrons within the body, a reaction producing gamma rays occurs. A scanner records these gamma rays and maps the area where the radioactive drug is located. For example, combining glucose (a common energy source in the body) with a radioactive substance will show where glucose is rapidly being used, for example, in a growing tumor.
- Bone scans are used to
create images of bones on a computer screen or on film. Doctors may order a
bone scan to determine whether a lung cancer has metastasized to the bones. In
a bone scan, a small amount of radioactive material is injected into the
bloodstream and collects in the bones, especially in abnormal areas such as
those involved by metastatic tumors. The radioactive material is detected by a
scanner, and the image of the bones is recorded on a special film for
permanent viewing.
- Sputum cytology: The
diagnosis of lung cancer always requires confirmation of malignant cells by a
pathologist, even when symptoms and X-ray studies are suspicious for lung
cancer. The simplest method to establish the diagnosis is the examination of
sputum under a microscope. If a tumor is centrally located and has invaded the
airways, this procedure, known as a sputum cytology examination, may allow
visualization of tumor cells for diagnosis. This is the most risk-free and
inexpensive tissue diagnostic procedure, but its value is limited since tumor
cells will not always be present in sputum even if a cancer is present. Also, noncancerous cells may occasionally undergo changes in reaction to
inflammation or injury that makes them look like cancer cells.
- Bronchoscopy: Examination of the airways by bronchoscopy (visualizing the airways through a thin, fiberoptic probe inserted through the nose or mouth) may reveal areas of tumor that can be sampled (biopsied) for diagnosis by a pathologist. A tumor in the central areas of the lung or arising from the larger airways is accessible to sampling using this technique. Bronchoscopy may be performed using a rigid or a flexible, fiberoptic bronchoscope and can be performed in a same-day outpatient bronchoscopy suite, an operating room, or on a hospital ward. The procedure can be uncomfortable, and it requires sedation or anesthesia. While bronchoscopy is relatively safe, it must be carried out by a lung specialist (pulmonologist or surgeon) experienced in the procedure. When a tumor is visualized and adequately sampled, an accurate cancer diagnosis usually is possible. Some patients may cough up dark-brown blood for one to two days after the procedure. More serious but rare complications include a greater amount of bleeding, decreased levels of oxygen in the blood, and heart arrhythmias as well as complications from sedative medications and anesthesia.
- Needle biopsy: Fine needle aspiration (FNA) through the skin, most commonly
performed with radiological imaging for guidance, may be useful in retrieving
cells for diagnosis from tumor nodules in the lungs. Needle biopsies are
particularly useful when the lung tumor is peripherally located in the lung and
not accessible to sampling by bronchoscopy. A small amount of local anesthetic
is given prior to insertion of a thin needle through the chest wall into the
abnormal area in the lung. Cells are suctioned into the syringe and are examined
under the microscope for tumor cells. This procedure is generally accurate when
the tissue from the affected area is adequately sampled, but in some cases,
adjacent or uninvolved areas of the lung may be mistakenly sampled. A small risk
(3%-5%) of an air leak from the lungs (called a pneumothorax, which can easily be
treated) accompanies the procedure.
- Thoracentesis: Sometimes
lung cancers involve the lining tissue of the lungs (pleura) and lead to an
accumulation of fluid in the space between the lungs and chest wall (called a
pleural effusion). Aspiration of a sample of this fluid with a thin needle
(thoracentesis) may reveal the cancer cells and establish the diagnosis. As
with the needle biopsy, a small risk of a pneumothorax is associated with this
procedure.
- Major surgical procedures: If none of the aforementioned methods yields a diagnosis, surgical methods must be employed to obtain tumor tissue for diagnosis. These can include mediastinoscopy (examining the chest cavity between the lungs through a surgically inserted probe with biopsy of tumor masses or lymph nodes that may contain metastases) or thoracotomy
(surgical opening of the chest wall for removal or biopsy of a tumor). With
a thoracotomy, it is rare to be able to completely remove a lung cancer, and both mediastinoscopy and thoracotomy carry the risks of major surgical procedures (complications such as bleeding, infection, and risks from anesthesia and medications). These procedures are performed in an operating room, and the patient must be hospitalized.
- Blood tests: While routine blood tests alone cannot diagnose lung cancer,
they may reveal biochemical or metabolic abnormalities in the body that
accompany cancer. For example, elevated levels of calcium or of the enzyme
alkaline phosphatase may accompany cancer that is metastatic to the bones.
Likewise, elevated levels of certain enzymes normally present within liver
cells, including aspartate aminotransferase (AST or SGOT) and alanine
aminotransferase (ALT or SGPT), signal liver damage, possibly through the
presence of metastatic tumor.
 Schematic illustration of a lung cancer located in the right upper lobe of the lung.
Next: What is staging of lung cancer? »
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