By Ted Gansler, MD, MBA, MPH
Most people's impression of pathology is based on the forensic pathologists in TV shows such as "CSI" (or, if you're my age, "Quincy, ME"). But for people facing cancer, there is another aspect of pathology to learn about - the testing that is done to find out whether an area of diseased tissue is benign (not cancer) or malignant (cancer).
Doctors often suspect that a person has cancer based on their physical exam findings and on the results of x-rays and scans. In the vast majority of cases, however, samples of cells (called cytology) or tissue samples (biopsies) must be tested to know for sure. And, if the tumor is cancerous, pathology testing will also determine what kind of cancer is present. This information is very important in guiding the treatment you receive, and in estimating your outlook for recovery and survival.
People receiving treatments for cancer usually get to know the teams of professionals who perform surgery and who prescribe and give their chemotherapy and radiation. On the other hand, you rarely meet the pathologists, technologists, and other laboratory professionals who test the biopsies, blood, and other specimens removed from your body. Learning about what they do with your samples can help you make informed decisions about your care.
Answering basic questions
Samples of tumors are tested to help answer questions such as:
- Is the tumor benign (not cancer) or malignant (cancer)?
- How far/where has the cancer spread? If you had surgery, was the main tumor removed completely?
- What kind of cancer is it? Is this a kind of cancer that is likely to shrink or disappear with radiation or chemotherapy? What medicines (including chemotherapy and targeted therapies) are likely to be most effective?
Regardless of how the sample is removed or how large it is, it will be sent to the pathology laboratory for testing. The kinds of tests that are done will depend on factors that include the size and location of the cancer and the kinds of treatment doctors are considering, but testing almost always starts with what is often called "routine histology." This involves viewing very thin (about 1/5000 of an inch) slices of tissue under a microscope. The samples are treated first with several chemicals, embedded in a block of wax so that very thin slices (called "sections") can be made, and then treated with special dyes that help the pathologist recognize features of normal and abnormal cells.
For many biopsies, all that is needed is the routine histology and interpretation of microscopic findings. In some cases, additional laboratory tests of biopsy samples are needed to be confident about the right diagnosis.
Professional expertise is key
Today, many medical laboratory tests (such as the level of certain chemicals in blood or urine samples) are highly automated. Biopsy results, though, are still determined by a person. The pathologist, who is a medical doctor, looks at features of the cells and how they are arranged in the tissue.
In many ways, a pathologist's approach to examining a biopsy is like a cardiologist listening to heart sounds or a dermatologist looking at a rash. These doctors all base their diagnostic conclusions on years of experience, on a thorough understanding of clinical science, and on knowledge of agreed-upon rules or criteria for classifying various diseases.
Knowing that results depend on humans rather than machines helps you understand how 2 pathologists examining the same biopsy specimen will occasionally report different diagnoses, and why it is sometimes useful to obtain a second or even third opinion in some cases.
A second opinion is helpful if the initial findings are inconclusive, or if the diagnosis appears to be a rare form of cancer that only a handful of pathologists can expertly recognize.
The surgeon or the oncologist may also suggest a second pathology opinion if the initial diagnosis does not seem to match the diagnosis they suspected based on the physical exam or x-ray tests. Another pathology opinion can also help when a different interpretation could change the treatment plan.
If you have doubts about your diagnosis, advice from a trusted clinician or the first pathologist is a good place to start.
On the cutting edge of cancer diagnosis
Did you know that many kinds of tumors can occur in each organ? For example, there are more than 40 kinds of ovarian tumors and more than 60 kinds of lymphoma. Do these differences matter? If you saw a "beware of dog" sign, wouldn't you want to know whether the canine in question is a Chihuahua or a Rottweiler?
Likewise, some subtypes of cancer have a much more serious prognosis than others. Even more importantly, knowing the precise type of cancer can help predict which kinds of treatment will be most effective. All of this information comes from pathology reports.
Over the past few decades, researchers have recognized that cancers that look the same under a microscope may have different changes in their chromosomes, DNA, RNA, and proteins, and that these changes can predict the likelihood of responding to certain medications. Targeted therapies, for instance, are effective only for cancers whose cells have the specific abnormality targeted by that drug.
In the past, a new anti-cancer drug would have been considered a failure if it helped only 5% of people with lung cancer, for example. But, if biopsy samples are available to identify which 5% of patients are likely to be helped, then the drug can be used very effectively.
Tests that look for these changes are part of a pathology examination. Although they are not necessary or available for some kinds of cancer, they are being used more and more for several common cancer types, such as breast cancer, lung cancer, leukemia, and lymphoma.
There is not nearly enough room on this page to describe all of the special tests used for every type of cancer. Fortunately, we already have information on the American Cancer Society website describing the usual tests for nearly every kind of cancer. Choose the section called "How is [fill in the type here] cancer diagnosed?" to find out how these routine and special tests influence a person's prognosis and treatment options. You can also learn more in our piece called "Testing Biopsy and Cytology Specimens for Cancer."
There are 2 national pathology organizations that I recommend for patients and their caregivers interested in understanding their pathology results more completely. Both the College of American Pathologists and the Association of Directors of Anatomic and Surgical Pathology provide background information about biopsies and pathology results.
Dr. Gansler is director of medical content for the American Cancer Society.