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How is Cancer Diagnosed?

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:

Biopsy

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 specialist.

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.

Metabolic Panel

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

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 is working.

Here are descriptions of some of the more common types of imaging tests:

Ultrasound

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.

Bone Scan

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.