Counting chromosomes for early detection

by Barbara Berg

If there’s one health matter most Americans understand, it’s heartburn. With restaurants serving up tremendous portions and antacid advertisements urging multiple trips to the buffet bar, it’s no wonder that more than 100 million Americans suffer from occasional episodes of this digestive distress. But for almost 2 million people, discomfort from heartburn—a condition caused by stomach-acid reflux—can mean chronic disease with sometimes-deadly consequences.

“Those television ads that talk about heartburn—they don’t know heartburn,” says Jim Moell, 74, of Everett, Wash., whose daily bouts of stomach acid washing into his upper digestive tract were setting the stage for cancer of his esophagus, the muscular tube that carries food from the throat to the stomach.

Plagued by chronic heartburn and an ulcer at the base of his esophagus, Moell sought help from Dr. Brian Reid, who was studying Barrett’s esophagus, a pre-cancerous condition caused by chronic acid reflux. Reid was banking on the power of genetic technology to save high-risk Barrett’s patients like Moell from an increasingly common, deadly form of cancer.

Luckily, Moell was in good hands.

Under Reid’s study, regular examination of the cells in Moell’s esophagus during the next few years revealed that his condition had developed into cancer. The cancer was detected so early that it couldn’t be seen with the naked eye. Moell had surgery to remove part of his esophagus and has been cancer-free for 13 years.

Thanks to the participation of hundreds of research volunteers like Moell, Reid and colleagues at Fred Hutchinson Cancer Research Center have completed a 15-year study demonstrating the success of a highly sensitive method for predicting a patient’s risk of esophageal cancer—a method that has already saved many lives.

Published last summer, the study shows that early DNA analysis of esophageal cells from patients with Barrett’s esophagus is so accurately predictive of cancer risk that most patients can be spared the painful biopsies every few months to monitor their condition. Those in the study who developed esophageal cancer had more than an 80 percent chance of survival, compared with a 5 percent survival rate for patients who do not have the kind of leading-edge surveillance Reid has developed.

In addition to saving lives, the results could have an impact on health-care costs by reducing unnecessary procedures. The technique may ultimately be extended to early detection of other types of cancer.

Dubbed the Seattle Barrett’s Esophagus Program, the study was initiated by Reid in 1983 at the University of Washington and moved to the Hutchinson Center in 1996.

Reid and his colleagues have worked with more than 800 patients to date in what is one of the most striking examples of how analyzing chromosomes—the spaghetti-like mass of DNA strands that contain the instructions to build an organism—can predict cancer risk.

The program is a web of interdisciplinary research, combining the strengths of scientists who manipulate DNA, epidemiologists who track risky behaviors, and physicians and surgeons from the Hutchinson Center and UW.

Barrett’s esophagus is a condition in which the flat cells lining the esophagus are replaced by abnormal, elongated cells due to constant exposure to stomach acid. The damaged cells of the esophagus must divide more frequently than normal to replace the wounded cells. Increased cell division means a greater likelihood that a cell might make a mistake while duplicating its chromosomes. Too many mistakes can lead to cancer.

In about 1 percent of Barrett’s patients each year, the condition progresses to a type of cancer called esophageal adenocarcinoma.

Esophageal cancer became Reid’s focus because the gastrointestinal tract was well suited to his research needs.

In 1975, Reid, finishing his Ph.D. in genetics at the University of Washington, was looking for a system that would allow him to study how cumulative assaults on a cell’s genetic material could cause cancer.

“I really believed that cancer was caused by genetic mechanisms,” says Reid, who completed his graduate work in the laboratory of Dr. Lee Hartwell, now president and director of the Hutchinson Center. “But the issue was, how can you prove that in the human body?”

Reid decided to enter medical school and find a specialty that would allow him to take his interests out of the lab and focus directly on cancer in the human body. Gastroenterology, the study of the digestive tract, immediately appealed to Reid as a system that might be amenable to study.

“The GI tract has a number of pre-malignant syndromes, biopsies of these tissues are safe and most patients don’t get cancer,” says Reid.

This makes it possible to follow the patients at risk for developing cancer over time, monitoring the cellular and genetic changes that occur.

Reid points out that when he began medical school, fiber-optic technology for visualizing the interior of the human body had just been developed. “Fiber optics made it easy to gain access to organs in a way that had never been possible before,” he says.

Reid’s interest in the genetic basis of cancer began in graduate school, where he studied how cells control the process of dividing in two. Using the bakers yeast Saccharomyces cerevisiae as model system, Hartwell’s research team later discovered that cells choose to divide or not based on a series of checkpoints, or gatekeepers. These cellular crossing guards effectively look both ways before the cell crosses to the next step in the division pathway, monitoring each step of the doubling process for potentially catastrophic mistakes. For example, if a mistake occurs while the cell is duplicating its chromosomes, a checkpoint halts cell division until the error is corrected.

Single-celled organisms like yeast are remarkably similar to animal cells, and checkpoints and other cell-division controls have not only been discovered in human cells, but have been shown to help protect cells from unrestrained, cancerous growth. When certain checkpoints are damaged, cells continue to divide even when their DNA—which holds the instructions for life—is full of errors.

In Barrett’s esophagus, Reid found his ideal system for mapping out the timeline of cancer progression. Only a fraction of patients with Barrett’s go on to develop cancer, and the course of the disease can be monitored by a direct look into the esophagus. Endoscopy—a procedure in which a slender, flexible fiber-optic tube is inserted through the mouth into the esophagus—allows doctors to obtain small tissue samples, or biopsies, from the esophagus at regular intervals and examine them for malignant growth. Reid could then begin to tease apart the cellular differences that cause this small subset of patients to develop cancer.

Reid and Dr. Peter Rabinovitch, a pathologist at UW, began using a technique called flow cytometry that illuminates chromosomes in the cell and permits them to be counted. Flow cytometry can be used to monitor cells from esophageal biopsies and sort them based on their DNA content, such that cells with abnormal amounts can be distinguished from their normal counterparts.

The advantage of flow cytometry is that doctors can determine whether cells have undergone significant genetic change, a key risk factor for cancer.

“While you can see differences in tissue type by examining biopsy samples microscopically, you can’t distinguish genetically different cells in a population of cells that appear to be identical,” says Dr. Mike Barrett, an investigator in Reid’s group. These “invisible” genetic differences provide definitive clues to whether a cell from a Barrett’s patient will become cancerous in a way that standard tissue analysis cannot. Two pathologists performing microscopic analysis of an esophageal biopsy might come to very different conclusions about the prognosis. Using highly accurate flow cytometry to examine the sample, there is no dispute. Analysis by flow cytometry gives observer agreement approaching 95 percent, Reid says.

The ability to accurately stage Barrett’s progression and predict risk of cancer has enormous implications for both health care costs and patient mortality due to unnecessary surgery. Abnormal DNA content detected by flow cytometry is a highly accurate predictor of progression to cancer. Reid’s group has shown that patients without such abnormalities do not develop cancer, and might be monitored by endoscopy, an expensive medical procedure, much less frequently than high-risk patients. The sensitive detection technique also holds promise for preventing unnecessary esophagectomies, the most lethal, commonly occurring surgery. “In low-volume institutions—those performing fewer than six esophagectomies a year —the mortality rate just from the surgical procedure is close to 20 percent,” Reid says. In contrast, in institutions that regularly perform the surgery, like UW, mortality is between 2 and 3 percent.

Barrett and others in Reid’s lab have taken the level of genetic analysis a step further by examining the specific DNA sequences that are altered in cells that progress to cancer. Not surprisingly, they include the very checkpoints Hartwell’s team discovered in yeast. The group is now using DNA microarrays, small chips that allow thousands of genes from an individual to be analyzed simultaneously, to follow the course of genetic changes in great detail.

Although early detection of esophageal cancer has made an enormous impact in patient care, prevention of cancer is the ultimate goal. “The ideal situation would be to find a low-cost way to prevent patients from ever developing Barrett’s esophagus,” Reid says.

Working with him in prevention is Dr. Tom Vaughan, an epidemiologist in the Hutchinson Center’s Public Health Sciences Division. Rather than looking inside cells, Vaughan and his colleagues ask whether what we eat or what medicines we take may heighten our cancer risk. Vaughan hopes to identify behaviors and environmental exposures that correlate with development of Barrett’s and esophageal cancer (see sidebar). “Because patients can be followed for long time periods and because the disease progresses through distinct stages, Barrett’s esophagus is almost unique as a system for understanding risks that predispose patients to disease development,” Vaughan says. In addition to surveillance by endoscopy, patients in the Barrett’s study are asked about their diet, use of medication and other behaviors. Vaughan’s group analyzes this data to determine whether specific behaviors contribute to cancer risk.

While excited about the advances made in his laboratory, Reid never loses sight of the patients, who both benefit from and contribute to the research. He sees patients one day each week and is committed to doing much of the counseling when patients are learning about their cancer risk. “I make sure to provide patients with information that they can really understand,” he says.

Reid also insists that new members of his laboratory grasp all facets of the research project. Barrett, a molecular biologist, has seen an endoscopy performed and regularly interacts with the clinical staff. “Brian wants everyone who joins the team to see every part of the process to get a sense of how complex it is,” Barrett says. “It’s important for me, as molecular biologist, to design studies with the people who are actually taking the biopsy samples.”

Even the patients know that they are part of a team that can make a difference. Says cancer-survivor Moell, “I joined Dr. Reid’s study because I thought that even if I couldn’t be helped, I might be able to help somebody else.”

Barbara Berg, Ph.D., is a science writer for the Fred Hutchinson Cancer Research Center.

Barrett’s esophagus: Who is at risk?

Barrett’s esophagus, a precancerous condition that affects the lining of the esophagus, occurs in approximately 10 percent of all people who experience chronic heartburn. About 5 to 10 percent of people with Barrett’s will develop esophageal cancer.

While a spicy meal may trigger the occasional episode of heartburn, daily bouts of acid reflux over long periods increase risk for developing Barrett’s esophagus. Risk factors for esophageal cancer include obesity, smoking and a diet high in fat and low in fruits and vegetables.

Where to get more information

More information about Barrett’s esophagus can be found on these Web sites:

• http://www.barrettsinfo.com
This is an informational Web site about Barrett’s esophagus created by Dr. Patricia Blount, David Cowan, and Dr. Brian Reid of the Hutchinson Center that provides a comprehensive overview of the disease and includes many informative figures and photos.

• http://www.fhcrc.org/science/phs/barretts/
The Hutchinson Center’s Seattle Barrett’s Esophagus Program maintains this Web site that includes links to scientific and news articles about the disease as well as general information for both patients and doctors.

How you can help support cutting-edge cancer research at the Hutchinson Center

You can support the groundbreaking work of research scientists like Brian Reid by donating to the Hutchinson Center. Private gifts provide financial support for new researchers and leading-edge studies with great potential for eliminating cancer and related diseases.

For more information, contact the Hutchinson Center at (800) 279-1618.