By Melissa Weber

In making the leap from possible detection of cancer to the crucial details involving stage, treatment, and prognosis, a cancer patient must trust someone he or she may never meet—the pathologist.

“The role of the pathologist is to make the diagnosis,” says Elaine S. Jaffe, MD, deputy chief, Laboratory of Pathology, National Cancer Institute, Bethesda, Maryland. “Because there are many different types of treatments for many different types of cancers, it’s important to make the right diagnosis so that the correct treatment can be delivered.

“It’s really a crucial starting point in the treatment of a cancer patient,” she adds.

Pathology, the study of the abnormalities that give rise to disease, has two main divisions—clinical and anatomic. Clinical pathology deals with the procedures performed on blood and other fluids or substances secreted or excreted by the body. The anatomical side of pathology, the focus of this article, examines tissues removed from the body by biopsy or resection.

A routine clinical examination may identify lesions or areas of the body that appear suspicious but rarely determines the presence of cancer, which requires a pathologic examination. In addition to determining presence, examination verifies type of cancer, advancement, if it has spread (metastasized) to other parts of the body, what the response will be to certain therapies, and the potential for recurrence. The pathology report (see sidebar) comprises standardized categories detailing a patient’s case that allow the medical team to determine the best treatment options.

Following the Tissue: Methods of Testing
Tissue from a biopsy (see sidebar), immediately sent to the pathology department, is examined first by the naked eye in a gross examination. The pathologist records its appearance and certain characteristics, which include size, weight, color, and texture.

Any tumor present is measured, as is the distance from the edge of the mass to the specimen’s edge. This “margin” of tissue determines if the entire tumor has been removed. A positive margin, meaning cancer cells continue to the edge of the tissue, may mean additional surgery; a negative margin means the cancer cells do not extend to the specimen’s edge and additional surgery may not be needed; and a close margin, which skirts the line between positive and negative, also suggests more surgery may be needed.

“After gross examination, the pathologist cuts the specimen into thin slices, and representative portions of the tumor tissue are chosen for preservation and testing,” explains Janet Arber, MD, a pathologist at Hoag Cancer Center, Newport Beach, California. “From there, the tissue is then fixed with formalin (a formaldehyde solution) in order to harden and fix the tissue in its current state.”

Fixation prevents degradation of the proteins within the cells and stops all cell activities, including cell division.

After overnight processing, the tissue is embedded in wax blocks from which thin sections (.005 mm—about one-tenth the width of a human hair) are shaved off the top, mounted on glass slides, and stained.

The pathologist recognizes abnormalities in the tissue by gross and microscopic examination, during which the stained tissue is examined under a conventional light microscope. A malignant tumor exhibits an increased number of cells that appear disorganized.

Immunohistochemistry
A widely used staining technique called immunohistochemistry (IHC) determines cell identity and function by identifying a specific antigen, a protein within the nucleus, cytoplasm, or on the surface of the cancer cell. Antibodies from mice or rabbits latch on to particular antigens (proteins) to detect if they are present in the cancerous tissue.

“Pathology today is not just the pathologist looking under a microscope and making a diagnosis,” says Dr. Jaffe. “There are many sensitive molecular and immunohistologic techniques that can be used.”

With more than 300 different types of tumors, each with its own biology, specialized tumor marker tests are used. Tumor markers—many of which are not specific to a certain type of cancer—are substances found in higher than normal amounts in the tissue, blood, or urine of patients with certain types of cancer.

Dr. Arber says breast tumors, for example, are tested to determine the presence of proteins such as estrogen receptor and progesterone receptor. Using the IHC test, Dr. Arber says a breast tumor-containing block is treated with protein-specific antibodies.

“If the protein is present, the antibody will bind and that part of the cell will be seen as a brown color. So if I’m testing a breast tumor for estrogen receptor and I look at the slide and see a brown color within all of the malignant cells, that indicates estrogen receptor positive.”

Pathologists may perform an IHC test called Ki-67 on a tumor to determine growth rate and how many cells are in the proliferation cycle. “If there are many cells staining positively for Ki-67, it could indicate a more aggressive tumor,” says Dr. Arber.

Molecular Testing
A gene-based diagnostic test called FISH (fluorescent in situ hybridization) is most commonly used as an adjunctive test in breast cancer but can also be used for prostate cancer, leukemia, lymphoma, and bladder cancer.

FISH, most often used in testing for HER2 gene amplification, uses fluorescent molecules to “paint” genes. These molecules, called probes, are portions of single-stranded DNA that are chosen to correspond with selected genes within DNA the pathologist wants to examine. The probes bind to a specific gene or segment of DNA, making it possible to determine how many copies of that particular gene are present in each cell.

“When we have molecular probes to detect genetic abnormalities, that enhances diagnostic accuracy,” explains Dr. Jaffe. “I think it’s remarkable the extent to which diagnoses that were based on routine histological and immunophenotypic methods have been found to have a central molecular abnormality. And in a sense, that confirms the scientific accuracy of the process.”

Following these tests and examinations, the patient can expect to receive his or her pathology report within three days. But Dr. Arber says rare tumors may need additional evaluation.

Getting a Second Opinion
When Karen Weed was diagnosed in 2001 with stage III uterine cancer, the Verona, Wisconsin, resident got a second opinion. “Management of cancer is a whole different ball game,” says the 43-year-old. “I made the decision that I wanted my case reviewed by doctors who work with gynecological cancers for a living.”

After examining Weed’s case, pathologists at the nearby University of Wisconsin Medical Hospital and Clinics determined that she had both ovarian and uterine cancer, and both were stage I. With her revised diagnosis, Weed says, “My prognosis got a whole lot better!” And today, two years later, Weed says she is cancer-free.

Dr. Jaffe says several situations warrant a second opinion, one of which is a pathologist having difficulty making a diagnosis.

“It’s very important that the clinician be involved in this situation. Different types of cancer tend to present in different ways, so when the clinician feels that the diagnosis does not fit the clinical situation, it would be a red flag.”

In addition, she says that, while a second opinion is appropriate for a rare condition, common cancers may also warrant a second look. Recently, researchers at Johns Hopkins Hospital reviewed tissue samples of nearly 6,000 men and found that one of every 71 cases of prostate cancer was misdiagnosed.

The need for an accurate diagnosis of every cancer patient demonstrates the importance of pathology laboratories and the pathologists who run them.
Often tucked away in an area of the hospital patients never see, Dr. Arber says even though pathologists don’t personally know patients, “we do have their best interest at heart.”