How Is Cancer Diagnosed?
There is only one way to obtain a definitive diagnosis of cancer—
by biopsy, which is a laboratory analysis of a tissue sample by an expert
physician called a pathologist. Cancer cells have special characteristics
that are consistently recognizable when viewed through a microscope.
Pathologists are trained to test tissues to identify the type of cancer,
where it originated and whether or not it has spread. Cancers are named
for their site of origin. For example, a patient who has had a colon cancer
removed and subsequently develops a recurrence in the liver does not have
liver cancer— this is colon cancer with liver metastasis. Lung cancer
is a cancer that starts in the lung, not a cancer which has spread to the lung.
Types of Test
Here are the different types of tests used in the diagnosis of cancer:
During a biopsy procedure a small tissue specimen from the area of concern
is removed for examination under a microscope. This can be done with a
hollow needle under a local anesthetic using ultrasound or CT guidance,
or may be performed through a scope. A number of flexible scopes can be
used to guide the biopsy procedure such as an endoscope into the stomach
(often referred to as an EGD or upper GI endoscopy), the colon (colonoscopy),
the bladder (cystoscopy), or the airways of the lungs (bronchoscopy).
Depending on the location of the suspected tumor in the body, a biopsy
procedure can be done by a pathologist, surgeon, radiologist or other
Bone Marrow Biopsy
A bone marrow biopsy takes tissue from the center of the bone for analysis.
Typically a hollow needle is placed into the back of the large bone in
the pelvic area called the posterior iliac crest, under either local anesthetic
or conscious sedation. The needle is inserted through a small incision.
Though preliminary results can be available in a day or two, an extensive
analysis can take two to three weeks.
Complete Blood Count
At Cancer Care Associates we're able to perform complete blood count
(commonly called a "CBC") with just a finger-stick and to obtain
a result within minutes. The test measures the levels of various blood
elements including number and subtypes of white blood cells, quantity
of red blood cells, and numbers of platelets. White blood cells fight
infection and when low in number place a patient at risk of infection.
Red blood cells carry oxygen and when low in number results in fatigue.
Platelets prevent or help stop bleeding. CBC results can help diagnose
cancer, or help with monitoring treatment side effects.
Chemistry (metabolic) panels measure a variety of organ functions. At Cancer
Care, our chem panel includes measurements of electrolytes, kidney function,
nutritional level, and potential damage to the liver and skeletal system.
The electrolytes include levels of sodium, potassium, chloride, and carbon
dioxide. Kidney function is measured by BUN and creatinine and high levels
are undesirable. Albumin, a protein made by the liver, will be low if
nutrition is poor or there is dysfunction of the liver. Liver function
tests also include bilirubin, transaminases (AST and ALT), and alkaline
phosphatase. Mild elevation of liver tests is common and usually doesn't
indicate disease. Persistently significant elevations are undesirable
and require evaluation. Alkaline phosphatase can also be elevated due
to skeletal system damage.
Tumor markers are substances that can be found in the body when cancer
is present. The classic tumor marker is a protein found in higher amounts
in the blood when a certain type of cancer is present. Other tumor makers
are found in urine or other body fluid, and some are found in tumors and
other tissue. The tumor marker may be made by the cancer cells themselves,
or by the body in response to cancer or other conditions. Most tumor markers
are proteins, but some newer markers are genes or other substances.
There are many different tumor markers. Some are linked only to one type
of cancer, while others can be found in many types of cancer.
To test for a tumor marker, the doctor most often sends a sample of the
patient's blood or urine to a lab. Sometimes a piece of the tumor
itself is tested for tumor markers.
Tumor markers alone are rarely enough to show that cancer is present. Most
tumor markers can be made by normal cells as well as by cancer cells.
Sometimes non-cancerous diseases can also cause levels of certain tumor
markers to be higher than normal. And not every person with cancer has
higher levels of a tumor marker.
This is why the clinical judgment of a medical oncologist is essential
for determining whether or not the use of a tumor marker will result in
better treatment for a patient. When a doctor looks at the level of a
tumor marker, he or she will consider it along with the patient's
history, physical exam, and other lab tests or imaging studies.
Imaging and Radiology
Doctors use imaging tests to make pictures (images) of the inside of the
body. Imaging tests can be used in many ways, including to look for cancer,
to find out how far it has spread, and to help determine if cancer treatment
Here are descriptions of some of the more common types of imaging tests:
An ultrasound uses high-frequency sound waves to visualize the inside of
the body. No radiation is involved. A probe (transducer) is placed over
an area of the body such as the breast or liver; radio waves are transmitted
through the body part, bouncing back and recorded. An ultrasound can detect
an abnormality of a body part and suggest whether or not it is cancer,
but is not proof that a cancer is present. A biopsy of the abnormal area
is the only way to establish without doubt that the abnormality is cancer.
Computed Tomography (CT)
Computer Axial Tomography uses low dose x-rays to image the body. Patients
lie on a moving platform which slides into an x-ray machine shaped like
a large donut. Within that structure an x-ray unit rotates around the
patient's body, creating computer generated images that produce a
3D view of the inside of the body.
Magnetic Resonance Imaging (MRI)
Another test that doesn't use x-ray, MRI stands for magnetic resonance
imaging. A patient lies on a moving platform that slides into a relatively
narrow tunnel that contains a very powerful magnet. A computer generates
a 3D view of the inside of the body by reading changes in the electromagnetic
fields of different internal structures. MRI is particularly useful for
evaluating the brain and spinal cord. It is also used to evaluate the breast.
Positron Emission Tomography (PET)
PET scan is a nuclear medicine test. A small amount of radioactive glucose
is injected into the vein and the scan measures differences in rate of
glucose uptake by different structures within the body. Following the
injection, the patient lies on a moving platform which passes through
a open circular structure and a computer generates a 3D picture. Although
a photo is made of the scan for the purpose of placement in a patient's
chart, the scan is actually read on a computer monitor, so that the image
can be rotated 360 degrees, permitting more accurate interpretation.
This is a nuclear medicine test and should not be confused with a bone
density x-ray which is used to diagnose osteoporosis. A bone scan requires
the injection of a small amount radioactive substance into the vein, which
then travels to areas of high bone activity. After several hours pictures
are taken with a special camera.
Mammogram (Breast Scan)
Mammogram use a very low dose of x-ray energy to image the breast to find
abnormal tissue (formed by the breast in reaction to cancer) and/or collections
of calcium in a pattern seen on the mammogram that is determined to be
suspicious by the radiologist.