Pathology is the “study and diagnosis of disease through examination of organs, tissues, bodily fluids, and whole bodies” -- a medical discipline that many people have heard of, but most may not clearly understand.

Unlike most other doctors, pathologists rarely deal directly with patients. Nonetheless, their work has an enormous impact on patients and their subsequent treatment.

We spoke with Duke pathologist Rex Bentley, MD, to learn more about pathology and its impact on cancer.

What do pathologists do?

In its broadest sense, pathologists study human disease. We examine tissue and body fluid specimens removed from patients and determine the diagnosis. We can also perform autopsies.

In smaller hospitals, pathologists may cover a broad range of procedures, while at large medical centers like Duke, pathologists are specialized in a specific area. I’m an anatomic pathologist, and I specialize in cancers of the breast and ovaries.

It is my job to determine if a tumor is malignant (cancerous) or benign. If the tumor is malignant, I will provide the physician with important details about the tumor, including its grade, stage, how aggressive it is, and how likely it will respond to particular therapies.

For example, with breast cancer, I test for estrogen receptors. This will determine if estrogen treatment will likely be effective. Also, I can determine if the tumor is HER2+ or HER2-. That distinction will help the physician choose the best course of treatment for the patient.

How do physicians get the tumor samples from the patient?

There are a number of ways we receive samples to study. With cancers of the blood, we obviously use blood tests. For bladder cancer, we can often study the urine. For cervical cancer, we use results from a Pap smear.

For other cancers, we take cells from the tumor with a needle that we can then study. Surgeons can also remove all or part of the tumor, which can then be studied.

How are samples analyzed? How long does it take?

Sometimes we receive a specimen to study while the patient is still in surgery, thus we need to move quickly. In these cases, we will freeze the tissue first, and then a very small section of the tissue is taken, placed on a slide, and stained so it can be viewed under a microscope.

The surgeon can receive a diagnosis within 15 minutes after removing the specimen. This enables the surgeon to make critical decisions during surgery, including how much of the tumor to remove and if he or she has removed the entire tumor.

When an immediate diagnosis isn’t required, the turn around time is usually 24 hours. We take the tissue, put it in formalin fixative to preserve it, and then organic solvents to remove the water from the tissue. The sample is then placed in hot melted wax. After it cools, we have a tissue embedded in wax and cut a very thin section of it. We stain it and put it on a slide.

This method provides a much higher-quality microscopic section than the freezing method and has the added advantage of preserving the tissue so we can go back and obtain additional sections if we later need to do any special tests.

The microscope is the absolute core piece of equipment. I use it day in and day out. The standard tool is the H&E (hematoxylin and eosin) stained slide, which has been used since the late 1800s. I would guess that 90 percent of my diagnoses are made using a microscope and slide.

How can you tell if a tumor is cancerous?

I know what normal, healthy tissues look like under a microscope. There are predictable patterns in the cells. When the tumor is malignant, it looks very different.

With breast cancer, the cells are not organized well. I can see changes going on in individual cells. In normal cells, the nuclei are the same size. In cancer cells, they vary in size.

I can also physically see cells dividing very quickly. I determine the stage by how far advanced the tumor is: how big it is and how far it has spread.

What is special about pathology at Duke?

Pathology at Duke is unique because of the broad range of subspecialty experts we have in the department, and the large number of specialized tests that we have available (molecular genetic tests, for example).

Most pathology departments don’t have this kind of expertise, and it is a real advantage for our patients.