Cancer Diagnosis
Cancer Diagnosis
Diagnosis
is the process of confirming the presence of cancer and obtaining the necessary information about the cancer to make treatment decisions. If you have signs and symptoms consistent with cancer or have had a positive screening test, your doctor will order one or more diagnostic tests that fall into the following three categories:
Laboratory Tests
While there are many different kinds of
laboratory tests
, the most common involve the analysis of a sample of blood. While some blood test results may be recorded as simply positive or negative, many are given a numerical value that is compared to a normal range of values, which take into account the inevitable variations from person to person. They also may be checked against changes from previous tests (doctors often refer to these results as changes from baseline).
Depending on their results, diagnostic tests often lead to additional testing. Except in rare cases, such as leukemia, there is no blood test that can definitively diagnose cancer or rule it out. Rather, blood tests are used to detect the indirect effects of cancer.
Physicians use
complete blood counts
to identify the harmful effects of a cancer or its treatment. For example, cancer that has metastasized to the bone marrow can impair the production of blood cells causing a detectable decrease in red cell, white cell, and platelet counts. Similarly, many chemotherapeutic drugs are toxic to the bone marrow and produce the same effects on cell counts.
Some blood tests detect abnormalities in particular organs. For example,
serum creatinine
tests detect abnormalities in the kidneys. Bone tumors can sometimes cause abnormally high levels of
alkaline phosphatase
, and liver cancer can cause abnormally high levels of some
liver enzymes
.
Tumor markers
are substances that can often be detected in higher-than-normal amounts in the blood, urine, or body tissues of people with certain types of cancer. Tumor markers are produced either by the tumor itself, by the body in response to the presence of cancer, or by certain benign (noncancerous) conditions. See the Focus box below for more information regarding tumor markers.
| Focus Box: Tumor Markers |
| Currently, the main use of tumor markers is to assess a cancer's response to treatment and to check for recurrence. Scientists continue to study the uses of tumor markers including their role in the early detection and diagnosis of cancer. Most tumor markers, however, are not sufficiently sensitive or specific to be routinely used for screening and diagnosis. The use of prostate specific antigen for the early detection of prostate cancer is widely used, but remains controversial. If you are being evaluated for cancer, you may wish to ask your doctor about the role of tumor markers in the diagnosis and treatment of your specific tumor. |
Table 2 briefly lists selected tumor markers, and the cancers with which they are associated.
|
Tumor Marker
|
Cancers
|
Benign Conditions
|
|---|---|---|
|
Alpha-fetoprotein (AFP)
|
Liver, testicular, or ovarian cancer; rarely stomach cancer
|
|
|
Carcinoembryonic antigen (CEA)
|
Colorectal cancer, melanoma, lymphoma, and cancers of the breast, lung, pancreas, stomach, cervix, bladder, kidney, thyroid, liver, and ovary
|
Inflammatory bowel disease,
pancreatitis
, and liver disease; Tobacco use can also contribute to higher-than-normal levels of CEA
|
|
Human chorionic gonadotropin (HCG)
|
Choriocarcinoma (a rare cancer of the uterus),
trophoblastic disease
(a rare cancer that develops from an abnormally fertilized egg), cancers of the testis, ovary, liver, stomach, pancreas, and lung
|
Pregnancy and marijuana use can also cause elevated HCG levels
|
|
Calcitonin
|
Medullary carcinoma
of the thyroid, lung cancers
|
NA
|
|
Prostate-specific antigen (PSA)
|
Prostate cancer |
Prostatitis
(inflammation of the prostate) and benign prostatic hyperplasia (BPH)
|
|
CA-125
|
Ovarian cancer, cancers of the uterus, cervix, pancreas, liver, colon, breast, lung, and digestive tract
|
|
|
Beta-2-microglobulin (B2M)
|
NA
|
|
|
Bladder tumor antigen (BTA)
|
Bladder cancer
|
NA
|
|
CA 19.9
|
Pancreatic cancer
|
Pancreatitis
|
Imaging Studies
Cancer is difficult to find, especially in its early stages, yet for some types of cancer the sooner it is caught, the better. Imaging techniques—methods of producing pictures of the body’s interior—are often extremely useful for finding early cancers far too small to detect by other means. Imaging can also be used to determine if and where the cancer has spread, to plan surgical and other forms of therapy, and to detect recurrences following treatment. While imaging studies can be highly suggestive of cancer, by themselves they are incapable of distinguishing benign from malignant tumors. A biopsy is required for this.
Imaging studies come in two basic varieties: those that use waves of electromagnetic energy or high energy particles (gamma rays, x-rays, radio waves, and positrons) and those that use high-pitched sound waves. Table 3 lists imaging tests commonly used to detect cancer.
|
Study
|
Means of Producing Images
|
|---|---|
|
Chest radiographs
|
X-rays
|
|
Bone radiographs
|
X-rays
|
|
Contrast studies
|
X-rays
|
|
Mammograms
|
X-rays
|
|
Computed tomography (CT) scans
|
X-rays
|
|
Radionuclide bone scans
|
Gamma rays
|
|
Magnetic resonance imaging (MRI)
|
Radio waves
|
|
Positron emission tomography (PET)
|
Positrons
|
|
Ultrasound
|
Sound waves
|
Chest and bone radiographs
are images created using x-rays. To create the image, x-rays are directed through the patient and onto photographic film. How the tissues appear on the x-ray has to do with their density. High-density tissue, such as bone, absorbs a lot of x-rays and appears white on the developed x-ray. Low-density tissue, such as the air in your lungs absorbs few or no x-rays and appears black. Tumors in the chest typically appear gray to white on the film. Cancer involving bone will appear even whiter than the surrounding normal bone tissue.
Mammograms are x-ray images of the breast. They can identify an abnormality and often suggest the likelihood of cancer, but mammograms cannot diagnose cancer. Click here to learn more about
mammograms.
Contrast studies
use special materials that efficiently absorb x-rays. This allows the creation of images that would otherwise not be visible with x-rays alone. A common example is an air-contrast barium enema, in which liquid contrast material containing barium is inserted into the rectum filling the rectum and colon. X-rays images clearly highlight the barium as its coats the mucosal lining.
Computed tomography (CT)
scans (previously called computerized axial tomography [CAT] scanning) also use x-rays to create images. However, unlike plain x-ray studies, the area of interest is imaged not as a whole, but as thousands of cross-sectional views. Data from each view is sent to a computer, which detects minute differences in tissue density and creates a composite image based on these differences. The result is a detailed and precise cross-sectional view of internal structures. Click here to learn more about
abdominal
and
head CT scans
.
Radionuclide bone scans
are images of the skeleton that highlight sites of bone metastases. To perform a radionuclide bone scan, the radiologist injects a radioactive substance into the blood, which is preferentially taken up by the actively dividing cancer cells. This area of increased cellular activity appears to a special camera outside the body as a “hot spot” in relation to the surrounding normal bone. Click here to learn more about
bone scans
.
Magnetic resonance imaging (MRI)
creates images using magnetic fields and radio waves. In MRI, the body is exposed to strong magnetic fields while tiny pulses of radiowaves are sent through the area of the body that is being studied. The radiowaves passing through the different tissues disturb the magnetic field, causing signals to be emitted. The signals are processed by a computer and translated into an image. Click here to learn more about
MRIs
.
While
positron emission tomography (PET)
is mostly used experimentally, it is sometimes useful in the evaluation of cancers for which the more common imaging studies have yielded questionable results. PET scanning uses special substances called isotopes to create images. Click here to learn more about
PET
.
An
ultrasound
uses high-frequency sound waves to create images, not unlike a submarine uses sonar to identify objects in its path. When these sound waves are bounced off interior structures, their pitch changes depending on the nature of the tissue reflecting them. The differential reflection of sound waves is used to create an image. Ultrasound is commonly used to detect certain abdominal tumors like ovarian, pancreatic, and liver. Click here to learn more about
abdominal ultrasounds
.
Tissue Biopsy
A definitive diagnosis of cancer ultimately requires a
biopsy
(sample) of the suspected cancerous tissue. Depending on their locations, tissue samples are usually collected by a surgeon and given to a pathologist, who examines them under a microscope in order to determine if it contains cancer or other worrisome cells. Tissue biopsies are typically performed in one of four ways:
- Superficial biopsy
- Fiberoptic biopsy
- Needle biopsy
- Surgical biopsy
A
superficial biopsy
is used when a cell or tissue sample is easily accessible on a body surface. They rarely require a surgeon and can be done during a simple office-based procedure. Examples include a skin biopsy or Pap smear.
During a
fiberoptic biopsy
, the doctor looks at areas inside the body through a thin, flexible tube equipped with a light source, video camera, and various surgical instruments. The tube is inserted directly into an organ or body cavity such as the abdomen, chest, bronchi, esophagus or intestines. The name of the test reflects the part of the body being studied. Upper endoscopy, for example, is used to study the upper gastrointestinal tract (esophagus, stomach and duodenum), while a bronchoscopy is used to evaluate the airways of the lungs. If the doctor sees a suspicious area during the test, he or she will take a biopsy and send it to the pathology lab for diagnosis.
In a
needle biopsy
, a needle is inserted into a suspected tumor and a small sample of cells or tissue is withdrawn. There are three types of needle biopsies:
- Fine-needle aspiration
- Core-needle biopsy
- Stereotactic core-needle biopsy
In
fine-needle aspiration
, fluid and cells from the tumor are sucked through a thin needle. This is commonly used to evaluate suspicious lumps in the breast. In
core-needle biopsy
, a larger needle is inserted, and a core of tissue is removed from the solid tumor.
Stereotactic core-needle biopsy
is a variation of core-needle biopsy in which a digital imaging camera is used to project an image of the tumor onto a screen and its three-dimensional coordinates (location in space) are calculated by a computer. This process allows the doctor to position the needle in exactly the right place in order to get the desired sample.
If a tumor is inaccessible through either endoscopic or needle biopsy, a doctor may choose to do a
surgical biopsy
. A surgical biopsy may be excisional or incisional. In an excisional biopsy, the surgeon removes the entire tumor and some surrounding normal tissue. In an incisional biopsy, the doctor removes just a portion of the tumor. If cancer is present, the entire tumor may be removed immediately or during another operation.
References
American Cancer Society. Cancer Facts & Figures 2003 . Atlanta, GA: American Cancer Society, Inc;2003.
Bast RC, Kufe DW, Pollock RE, et al. Eds. Cancer Medicine . 5th ed. Hamilton, ON: Decker Inc; 2000.
Cancer. Merck Manual of Medical Information website. Available at: http://www.merck.com/mrkshared/mmanual%5Fhome/contents.jsp . Accessed March 25, 2003.
Defining cancer. National Cancer Institute website. Available at: http://www.cancer.gov/cancertopics/what-is-cancer . Accessed August 1, 2008.
Detailed guide. American Cancer Society website. Available at: http://www.cancer.org/ . Accessed August 1, 2008.
Finley RS, Balmer C. Concepts in Oncology Therapeutics . 2nd ed. Bethesda, MD: American Society of Health-System Pharmacists;1998.
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