Sanford Markowitz, M.D., Ph.D.
cap001.pngDr. Markowitz is also Ingalls Professor of Cancer Genetics in the Department of Medicine (Hematology-Oncology) and the Ireland Cancer Center, with coappointment in the Department of Molecular Biology, at Case Western Reserve University School of Medicine and an attending physician at University Hospitals of Cleveland. He received his B.A. degree in physics and chemistry from Harvard University. He received his M.D. and his Ph.D. degrees in cell biology from Yale University, where he worked with Vincent Marchesi. Dr. Markowitz did clinical training in internal medicine at the University of Chicago and in medical oncology at the National Cancer Institute, where he also did postdoctoral research in the laboratory of John Minna.

Bert Vogelstein, M.D.
cap002.pngCancer represents a cellular insurrection. Tumors form when a renegade cell accumulates mutations that allow it to reproduce without restraint and defy the molecular signals that tell it to stop. Over the past two decades, Bert Vogelstein and his team have uncovered the specific genes and mutations responsible for colorectal cancer and established a genetic model for cancer progression that has enhanced our understanding of the formation and development of all cancers. They are now using this knowledge to develop diagnostic tests for identifying individuals at risk for developing colon cancer and to search for new treatments for the disease.
Although he majored in math as an undergraduate, Vogelstein chose to pursue a medical degree so that he could focus on problems in human health. One of his first patients was a four-year-old with leukemia. “Here was this little girl with a disease that we knew almost nothing about,” he says. “It was very frustrating.” That feeling of helplessness drove Vogelstein to the lab, where he hoped he could make sense of cancer.

To get a handle on the molecular changes that drive malignancy, Vogelstein turned to studies of colorectal cancer. He chose this cancer, in part, because various forms of colorectal tumors can be obtained for genetic analysis. Vogelstein hoped to find evidence that colon cancers can be caused by the loss of a tumor suppressor, a gene that in normal cells acts as a molecular brake to control division. Tumor suppressors were high on the list of suspects because cancer cells frequently contain chromosomes that are broken or missing large chunks. These deleted regions, Vogelstein thought, were likely to harbor genes that normally restrict cell proliferation. The problem was that, at that point in time, tumor-suppressor genes were hypothetical; no one had yet identified a particular example.

Surprisingly, Vogelstein’s first search turned up TP53, a gene that had not been known to be altered in cancers and was thought to work in an opposite fashion from a tumor-suppressor gene, stimulating rather than inhibiting growth. But Vogelstein and his students provided incontrovertible evidence that TP53 really was the tumor-suppressor gene on chromosome 17 that they had been searching for. In colon cancer cells, both copies of TP53 were disabled; if one copy had been deleted, the other always harbored an inactivating mutation. They subsequently found that TP53 was involved not only in colon cancers, but in most types of human cancer, suggesting that the gene might be a common denominator for human cancers. This stimulated a revolution in cancer research: more than 20,000 mutations of TP53 have been identified in human cancers since Vogelstein’s first report.

Vogelstein then joined forces with Kenneth Kinzler, who started out as a graduate student in Vogelstein’s lab and is now a professor at Johns Hopkins. Working together, the researchers identified additional genes involved in colon cancers. One of the most important of these was APC. Vogelstein and Kinzler showed that mutations of APC occurring in single colorectal epithelial cells are the initiating events in colorectal tumors, starting off the process and leading to the formation of benign tumors (adenomas). Furthermore, patients who inherit a mutation in APC develop a disease called familial adenomatous polyposis and develop hundreds or thousands of benign tumors throughout their colon and rectum. The team also discovered other genes that cause familial forms of colorectal cancers, including several that, when compromised, destroy the cell’s ability to repair mistakes in its DNA. They have also identified genes, such as PIK3CA, that, when mutated, help convert benign tumors to malignant tumors.

Many of Vogelstein’s current research projects are aimed at devising less invasive ways to diagnose cancer early and at discovering therapeutic approaches that will wipe out tumors by exploiting the new knowledge of cancer biology. His lab has developed sensitive blood tests that are now used in the clinic to identify patients with inherited mutations in genes known to be involved in colorectal cancer. Vogelstein and his colleagues are also exploring experimental treatments. For example, they’ve used an oxygen-hating, soil-dwelling bacterium to thwart tumor growth in animals with cancer. Because tumors grow so quickly, they tend to outrun their blood supply, leaving certain areas low in oxygen. Microbes that thrive in the absence of oxygen can penetrate tumors, proliferate rapidly, and kill the cancer cells.

Dr. Vogelstein is also Clayton Professor of Oncology and Pathology and Director of the Ludwig Center for Cancer Genetics and Therapeutics at the Sidney Kimmel Comprehensive Cancer Center of the Johns Hopkins University School of Medicine.

March 3, 2008, Howard Hughes Medical Institute – Some colon cancers are destined to spread to the liver and other parts of the body, whereas others are successfully treated by surgical removal of the tumor. Now, Howard Hughes Medical Institute investigators have found that the ability of a colon tumor to metastasize arises early in its development.

Those colon cancers that spread carry the ability to metastasize from the time they become cancerous, the researchers found. They don’t need to acquire any new genetic mutations to become metastatic. The research also suggests that once a colon carcinoma develops, if it is going to spread outside the colon, it will do so in less than two years.

“Our research implies that the genetic machinery that causes metastases is hard-wired into the tumor from the beginning.”
Sanford Markowitz

“The ability to metastasize is hard-wired into this group of tumors in the colon,” said Sanford Markowitz, a Howard Hughes Medical Institute investigator at Case Western Reserve University. “It isn’t something that happens after a cancer cell wanders off and leaves the colon.”

Markowitz and his colleagues published their findings in the Proceedings of the National Academy of Sciences on March 3, 2008.

Colon cancer is the second leading cause of cancer mortality in the United States, causing about 60,000 deaths annually. But there are many more cases of colon cancer that are cured by surgical removal of the tumor. Markowitz and his team wanted to understand the genetic differences between the two types.

“It’s clear that colon cancer comes in two very different varieties,” said Markowitz, who led the study. “With one variety, the surgeon cuts it out and the individual is cured. With the other variety, the surgeon cuts it out but the disease still spreads, and despite our best efforts the individual succumbs to the disease. So you have two hugely different biological behaviors that are literally the difference between life and death. And we wanted to know if we could find a genetic basis for that difference.”
To do so, the team compared the DNA of primary colon tumors to the DNA of tumors in the liver that had spread from the colon – the metastases. Markowitz said he was shocked to discover that, in 7 of 10 patients, there were no new mutations in the liver tumors. That means the ability of those tumors to spread from the colon was hard-wired from their inception.

In the tumors from the other three patients, a few new genetic mutations appeared in the liver metastases. But none of the mutations appeared in more than one patient. “My guess is that these mutations are noise, that they aren’t responsible for the metastases,” said Markowitz.

The project drew on advances in DNA sequencing technology and collections of tumor samples from patients treated by Markowitz. The DNA sequencing was begun in the laboratory of Bert Vogelstein, a Howard Hughes Medical Institute investigator at the Kimmel Cancer Center at Johns Hopkins. Vogelstein’s laboratory sequenced all of the DNA of more than 18,000 genes in each of the tumor samples. The sequenced genes were drawn from RefSeq, a compendium of 18,191 genes that represents the gold-standard in the field and is estimated to contain more than 90 percent of the coding information in the human genome.

Last October, the same team published a landmark paper in Science that surveyed all of the genetic mutations in samples of colon and breast tumors. That study found that approximately 280 candidate genes give rise to colon and breast cancer.

The new research focused exclusively on metastatic colon cancer. The study examined point mutations – single letter changes in DNA base-pair sequences – in the tumor samples.

Because the researchers know how quickly such random mutations accumulate, they could estimate how long it took each colon tumor to develop and metastasize. “We can use the mutations as a molecular clock,” said Markowitz. The clock ticks at a rate of about one mutation every two years.

Markowitz and his team discovered that it takes about 17 years for a small colon polyp – also called an adenoma, the first, non-deadly stage of colon cancer – to develop into a more dangerous advanced carcinoma. The team determined this by comparing, within individual patients, the DNA of adenomas to the DNA of adjacent carcinomas that developed later. “The adenomas just kind of percolate along,” said Markowitz. “It takes them a good while to figure out how to become a carcinoma, which is a cancer that can metastasize.”

But if a tumor develops into a carcinoma with the ability to metastasize, it will progress to metastasis quickly. This transformation occurs within about two years, before another mutation can develop.

The next stage of the project will compare the DNA of colon tumors in patients with metastatic disease to colon tumors from patients who don’t experience metastases. “Our research implies that the genetic machinery that causes metastases is hard-wired into the tumor from the beginning. We now want to find out what that genetic machinery looks like,” said Markowitz.

Understanding the hard-wired genetic defects that cause metastases could have implications for patient care. Once such mutations are known, testing for them could highlight patients at high-risk of metastases and help guide treatment decisions.