Ovarian Cancer Tumors Can Grow For Ten Years Or More Before Being Detected By Today’s Blood Tests

A new mathematical model developed by Stanford University School of Medicine scientists finds that ovarian cancer tumors can grow for 10 years or longer before currently available blood tests will detect them.

A new mathematical model developed by Stanford University School of Medicine scientists indicates that tumors can grow for 10 years or longer before currently available blood tests will detect them. The analysis, which was restricted to ovarian cancer tumors but is broadly applicable across all solid tumor types, was published online November 16 in Science Translational Medicine.

“The study’s results can be viewed as both bad and good news,” said Sanjiv “Sam” Gambhir, M.D., Ph.D., professor and chair of radiology and the study’s senior author. Sharon Hori, Ph.D., a postdoctoral scholar in Dr. Gambhir’s laboratory, is the lead study author.

The mathematical model developed by Dr. Sam Gambhir’s lab shows that it would be possible to detect tumors years before they grow big enough to metastasize if researchers can develop the right biomarkers.

The bad news, as explained by Dr. Gambhir, is that by time a tumor reaches a detectable size using today’s available blood tests, it is likely to have metastasized to other areas of the body, making it much more deadly than if it had been caught earlier. “The good news is that we have, potentially, 10 or even 20 years to find the tumor before it reaches this size, if only we can improve our blood-based methods of detecting tumors,” said Dr. Gambhir. “We think our mathematical model will help guide attempts to do that.”

The study advances previous research about the limits of current detection methods. For instance, it is strikingly consistent with a finding reported two years ago by Stanford biochemistry professor Patrick Brown, M.D., Ph.D., that current ovarian cancer tests could not detect tumors early enough to make a significant dent in the mortality rate. There is a push to develop more-sensitive diagnostic tests and find better biomarkers, and Dr. Gambhir’s new model could be an essential tool in this effort. For the first time, the new model connects the size of a tumor with blood biomarker levels being shed by that tumor.

To create their model, Drs. Gambhir and Hori used mathematical models originally developed to predict the concentration of drugs injected into the blood. The investigators linked these to additional models of tumor cell growth.

Tumors do not secrete drugs, but they can shed telltale molecules into surrounding tissue, from which those substances, known as “biomarkers,” diffuse into the blood. Some biomarkers may be made predominantly by tumor cells.  These substances can be measured in the blood as proxies for a tumor.

Some biomarkers are in wide use today. One is the well-known PSA (prostate specific antigen) for prostate cancer. Another example of a biomarker is CA-125 (cancer antigen 125) for ovarian cancer. But these and other currently used blood tests for cancer biomarkers were not specifically developed for early detection, and are generally more effective for relatively noninvasive monitoring of the progress of a late-stage tumor or tumor response to treatment. That is, rising blood levels of the substance may indicate that the tumor is growing, while declining levels may indicate possible tumor shrinkage.

Both CA-125 and PSA are also produced, albeit in smaller amounts, by healthy tissue, complicating efforts to detect cancer at an early stage when the tumor’s output of the biomarker is relatively low.

The new mathematical model employs separate equations, each governing the movement of a biomarker from one compartment into the next. Into these equations, one can plug known values — such as how fast a particular type of tumor grows, how much of the biomarker a tumor cell of this type sheds per hour, and the minimum levels of the biomarker that must be present in the blood for a currently available assay to detect it.

As a test case, Drs. Gambhir and Hori chose CA-125, a well-studied biomarker which is shed into the blood by ovarian cancer tumors. Ovarian cancer is a notorious example of a condition for which early detection would make a significant difference in survival outcomes.

CA-125 is a protein made almost exclusively by ovarian tumor cells. The well-known pharmacokinetics, metabolic fates (typical amounts secreted by an ovarian cell), typical ovarian tumor growth rates, and other properties of CA-125 make the biomarker an excellent candidate for “road testing” with Gambhir and Hori’s model. CA-125 is by no means the ideal biomarker, said Dr. Gambhir, while noting that it can still be used to better understand the ideal properties of biomarkers for early ovarian cancer detection.

Applying their equations to CA-125, Drs. Gambhir and Hori determined that an ovarian cancer tumor would need to reach a size of approximately 1.7 billion cells, or the volume of a cube with a 2-centimeter edge, before the currently available CA-125 blood test could reliably detect it. At typical tumor-growth rates, it would take a single cancer cell approximately 10.1 to 12.6 years of development to become a tumor containing 1.7 billion cells.

The model further calculated that a biomarker otherwise equivalent to CA125 — but shed only by ovarian tumor cells — would allow reliable detection within 7.7 years, while the tumor’s size would be that of a tiny cube about one-sixth of an inch high.

In the last decade, many potential new biomarkers for different forms of cancers have been identified. There’s no shortage of promising candidates — six for lung cancer alone, for example. But validating a biomarker in large clinical trials is a long, expensive process. So it is imperative to determine as efficiently as possible which, among many potential tumor biomarkers, is the best prospective candidate.

“This [mathematical] model could take some of the guesswork out of it,” Gambhir said. He also stated:

“It [the mathematical model] can be applied to all kinds of solid cancers and prospective biomarkers as long as we have enough data on, for instance, how much of it a tumor cell secretes per hour, how long the biomarker can circulate before it’s degraded and how quickly tumor cells divide. We can tweak one or another variable — for instance, whether a biomarker is also made in healthy tissues or just the tumor, or assume we could manage to boost the sensitivity of our blood tests by 10-fold or 100-fold — and see how much it advances our ability to detect the tumor earlier on.”

There are new detection technologies capable of detecting biomarkers at concentrations as low as a few hundred molecules per milliliter (1-cubic centimeter) of blood. In 2009, Dr. Gambhir and his colleagues reported on one such developing technology: “magneto-nanosensors” that can detect biomarkers with a 100-fold greater sensitivity than current methods.

Better biomarker detection alone might allow ovarian cancer tumor detection at the 9-year point, said Gambhir.

A second priority is to come up with new and better biomarkers. “It’s really important for us to find biomarkers that are made exclusively by tumor cells,” Dr. Gambhir said.

Under the right conditions (a highly sensitive assay measuring levels of a biomarker that is shed only by cancer cells), Gambhir stated, the model predicts that a tiny tumor with a volume equivalent to a cube less than one-fifteenth of an inch (or 1.7 millimeters) on a side could be detected.

Dr. Gambhir is also the Virginia and D.K. Ludwig Professor in Cancer Research and director of the Molecular Imaging Program at Stanford, the director of the Canary Center at Stanford for Cancer Early Detection, and a member of the Stanford Cancer Institute.

The study was funded by the Canary Foundation and the National Cancer Institute.

Sources:

• Hori S, Gambhir S, Mathematical Model Identifies Blood Biomarker–Based Early Cancer Detection Strategies and Limitations. Sci. Transl. Med. 3, 109ra116 (2011).

• New model establishes guidelines for earlier cancer detection, Press Release, Stanford School of Medicine, November 16, 2011.

New Study Shows Four-Year Window for Early Detection of Ovarian Cancer

A new study by Howard Hughes Medical Institute researchers shows that most early stage ovarian tumors exist for years at a size that is a thousand times smaller than existing tests can detect reliably.  But the researchers say their findings also point to new opportunities for detecting ovarian cancer—a roughly four-year window during which most tumors are big enough to be seen with a microscope, but have not yet spread.

Tiny Early-Stage Ovarian Tumors Define Early Detection Challenge

Currently available tests detect ovarian cancer when it is about the size of the onion in the photograph. To reduce ovarian cancer mortality by 50 percent, an early detection test would need to be able to reliably detect tumors the size of the peppercorn. (Photo Source: Patrick O. Brown, Howard Hughes Medical Institute Investigator, Research News Release, July 28, 2009)

A new study by Howard Hughes Medical Institute researchers shows that most early stage ovarian tumors exist for years at a size that is a thousand times smaller than existing tests can detect reliably.

But the researchers say their findings also point to new opportunities for detecting ovarian cancer—a roughly four-year window during which most tumors are big enough to be seen with a microscope, but have not yet spread.

“Our work provides a picture of the early events in the life of an ovarian tumor, before the patient knows it’s there,” says Howard Hughes Medical Institute researcher Patrick O. Brown. “It shows that there is a long window of opportunity for potentially life-saving early detection of this disease, but that the tumor spreads while it is still much too small to be detected by any of the tests that have been developed or proposed to date.”

According to the American Cancer Society, some 15,000 women in the United States and 140,000 women worldwide die from ovarian cancer each year. The vast majority of these deaths are from cancers of the serous type, which are usually discovered only after the cancer has spread.

“Instead of typically detecting these cancers at a very advanced stage, detecting them at an early stage would be enormous in terms of saving lives,” says Brown, who is at Stanford University School of Medicine. Early detection would enable surgeons to remove a tumor before it spreads, he adds.

The article—co-authored by Chana Palmer of the Canary Foundation, a nonprofit organization focused on early cancer detection—was published July 28, 2009, in the open access journal PLoS Medicine.

“Like almost everything with cancer … the more closely you look at the problem, the harder it looks,” Brown says. “That’s not to say that I don’t believe it’s a solvable problem. It’s just a difficult one.” — Patrick O. Brown, M.D. Ph.D.

Patrick O. Brown, M.D. Ph.D., Howard Hughes Medical Institute Investigator, Stanford Univ. School of Medicine

“Like almost everything with cancer … the more closely you look at the problem, the harder it looks,” Brown says. “That’s not to say that I don’t believe it’s a solvable problem. It’s just a difficult one.”

In the quest to develop early detection methods for ovarian cancer, Brown says, science hasn’t had a firm grasp on its target. So he and Palmer took advantage of published data on ovarian tumors to generate a better understanding of how the cancer progresses in its earliest stages.

The team analyzed data on serous-type ovarian tumors that were discovered when apparently healthy women at high genetic [BRCA1 gene mutation] risk for ovarian cancer had their ovaries and fallopian tubes removed prophylactically. Most of the tumors were microscopic in size; they were not detected when the excised tissue was examined with the naked eye.

The analysis uncovered a wealth of unexplored information. Thirty-seven of the early tumors had been precisely measured when they were excised – providing new details about the size of the tumors when they were developing prior to intervention, Brown says. By extrapolating from this “occult” size distribution to the size distribution of larger, clinically evident tumors, the researchers were able to develop a model of how the tumors grew and progressed. “We are essentially trying to build a story for how these tumors progress that fits the data,” Brown explains.

Among the study’s findings:

• Serous ovarian tumors exist for at least four years before they spread.

• The typical serous cancer is less than three millimeters across for 90 percent of this “window of opportunity for early detection.”

• These early tumors are twice as likely to be in the fallopian tubes as in the ovaries.

• To cut mortality from this cancer in half, an annual early-detection test would need to detect tumors five millimeters in diameter or less – about the size of a black peppercorn and less than a thousandth the size at which these cancers are typically detected today.

Brown’s lab is now looking for ways to take advantage of that window of opportunity to detect the microscopic tumors and intervene before the cancer spreads.

One strategy the laboratory is pursuing is to examine tissues near the ovaries, in the female reproductive tract, for protein or other molecular markers that could signify the presence of cancer. Brown says answering another question might also prove helpful: whether there is any reliable flow of material from the ovaries and fallopian tubes through the uterus and cervix into the vagina—material that might be tested for a specific cancer marker.

Despite science’s broad understanding of cancer at a molecular level, it has been challenging to identify simple molecular markers that signal the presence of early disease. One current blood marker, CA-125, has proven useful in monitoring later-stage ovarian cancer, but it has not been helpful for early detection. So Brown’s lab is also looking for biomarkers that are present only in ovarian tumors and not in healthy cells, instead of relying on tests that look for unusually high levels of a molecule that is part of normal biology (like CA-125).

The researchers are doing extensive sequencing of all messenger RNA molecules (which carry information for the production of specific proteins) in ovarian cancer cells, searching for evidence of proteins in these cells that would never be found in non-cancer cells. These variant molecules could be produced as a result of chromosome rearrangements—when the genome is cut and spliced in unusual ways—in ovarian cancers. “It’s a long shot,” says Brown, “but it’s important enough to try.”

Source: Tiny Early-Stage Ovarian Tumors Define Early Detection Challenge, Research News, Howard Hughes Medical Institute, July 29, 2009 [summarizing Brown PO, Palmer C, 2009 The Preclinical Natural History of Serous Ovarian Cancer: Defining the Target for Early Detection. PLoS Med 6(7): e1000114. doi:10.1371/journal.pmed.1000114].

Symptom Screening + CA-125 Blood Test = Better Detection of Early Stage Ovarian Cancer

” …Research has found that when used alone, a simple four-question symptom-screening questionnaire and the CA125 ovarian-cancer blood test each detect about 60 percent of women with early-stage ovarian cancer and 80 percent of those with late-stage disease. This study found that when used together, the questionnaire and blood test may boost early-detection rates to more than 80 percent and late-stage detection rates to more than 95 percent. …”

“Women’s reports of persistent, recent-onset symptoms linked to ovarian cancer – abdominal or pelvic pain, difficulty eating or feeling full quickly and abdominal bloating – when combined with the CA125 blood test may improve the early detection of ovarian cancer by 20 percent, according to new findings by researchers at Fred Hutchinson Cancer Research Center published online today in CANCER.

Research has found that when used alone, a simple four-question symptom-screening questionnaire and the CA125 ovarian-cancer blood test each detect about 60 percent of women with early-stage ovarian cancer and 80 percent of those with late-stage disease. This study found that when used together, the questionnaire and blood test may boost early-detection rates to more than 80 percent and late-stage detection rates to more than 95 percent.

‘Of course, it is the increase in the detection of early-stage disease that is the most exciting,’ said lead author M. Robyn Andersen, Ph.D., an associate member of the Public Health Sciences Division at the Hutchinson Center. Cure rates for those diagnosed when the disease is confined to the ovary are approximately 70 percent to 90 percent. However, more than 70 percent of women with ovarian cancer are diagnosed with advanced-stage disease, when the survival rate is only 20 percent to 30 percent.

‘This research suggests that if a woman has one or more symptoms that are new for her, having begun within the past year, and if the symptoms happen nearly daily or at least 12 times a month, that may well be a signal to go in and discuss those symptoms with her doctor,’ Andersen said. ‘It’s probably not going to be ovarian cancer, just as most breast lumps are not breast cancer, but it’s still a sign that it might be worth checking with her doctor to see if a CA125 blood test and transvaginal ultrasound may be appropriate.’

Assessing the symptoms included in the symptom-screening index may already be done by some doctors based on a consensus statement issued last year by the National Institutes of Health. The researchers hope their symptom index will help doctors know which among their patients who complain of symptoms such as abdominal swelling and pelvic pain might have cancer.

The symptom-screening index, developed in 2006 by paper co-author Barbara A. Goff, M.D., professor and director of Gynecologic Oncology at the University of Washington School of Medicine, is not used proactively in clinical general practice, but Andersen and colleagues are conducting a pilot study to assess the value of using it as a screening tool among normal-risk women as part of their routine medical-history assessment.

For the just-published study, the researchers administered the symptom questionnaire to 75 women about to undergo surgery for pelvic masses who were later diagnosed with ovarian cancer (the case group), and 254 healthy women at high risk for ovarian cancer due to a family history of the disease (the control, or comparison, group). The cases were recruited through Pacific Gynecology Specialists at Swedish Medical Center in Seattle, and the controls were recruited through the Ovarian Cancer Early Detection Study, a joint project of the Hutchinson Center and the Marsha Rivkin Center for Ovarian Cancer Research.

The National Institutes of Health/National Cancer Institute, the Marsha Rivkin Center for Ovarian Cancer Research and the Canary Foundation supported this research.”

[Quoted Source: Symptom screening plus a simple blood test equals a 20 percent jump in early detection of ovarian cancer, Fred Hutchinson Cancer Research Center News Release, June 23, 2008.]