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One-drop cancer test promising but imperfect

By Kosho Yamazaki / Yomiuri Shimbun Staff Writer A recently developed method of diagnosing 13 kinds of cancer from a single drop of blood can lead to early detection of the disease. The relatively inexpensive test puts less burden on patients, but it still needs further improvement in accuracy.

The new blood test was developed by a team comprising researchers from the National Cancer Center Japan in Tokyo and other entities. They began a clinical test of the method this month. Until now, there has been no test that can detect so many kinds of cancer at one time.

The test builds hope for treatment at an early stage to reduce cancer deaths, and is also expected to cut down on medical expenses. The team plans to ask the government to put it into practical use as early as within three years.

miRNA key to test

“By using a blood sample taken for a comprehensive medical examination or other checkups, this new test can detect which type of cancer a patient has from an early stage. It is an unprecedented examination method,” said Takahiro Ochiya, chief of the Molecular and Cellular Medicine Division at the National Cancer Center Research Institute, who leads the team for the new test.

The researchers focused on a molecular substance called microRNA, or miRNA (see below), as the key to the new technologies. Cancer cells secrete specific kinds of miRNA, which differ depending on the type of cancer.

The team began the research in 2014. After obtaining ¥8 billion of government funds, the team examined secretion patterns of types of miRNA by using blood samples of 40,000 elderly individuals that had been preserved by the institute and other entities. The samples included those from cancer patients as well as people without cancer.

The team successfully detected the patterns of breast, colorectal, pancreatic, biliary tract, esophageal, liver, ovarian, lung, stomach, bladder and prostate cancers, which are major cancers among Japanese people.

They also detected patterns for glioma, which accounts for 30 percent of brain tumors, as well as a rare bone cancer and a type of soft tissue tumor.

The progression of cancer is indicated in four different stages from the early Stage 1 to the most advanced Stage 4.

The researchers were able to diagnose patients with breast cancer — including those at Stage 1 — by analyzing five types of miRNA, with 97 percent accuracy. The team also detected other kinds of cancer with at least 95 percent accuracy.

The quality of miRNAs in blood changes over time. Therefore, the researchers will examine “fresh blood” from about 3,400 people to finalize the verification of the blood test’s accuracy in the clinical trials that began this month.

The main purpose of the new test is to discover cancer at an early stage by a simple method. Currently, various other types of cancer tests are already in use.

One method is to measure “tumor markers” in blood. However since tumor markers are proteins produced when cancer cells die and dissolve, they cannot be detected until the cancer has grown to some extent.

Five types of cancers — breast, stomach, colorectal, lung and cervical — that are often included in medical checkups offered by companies and local governments are covered by a wide range of medical departments such as breast oncology and gastroenterology. X-ray machines, endoscopes and so on are used to check for those cancers, and the performance of such devices has been improving.

However, Tomio Nakayama, director of the epidemiology statics department at Osaka International Cancer Institute, points out, “Doctors who can skillfully read images [of test machines] to discover cancers are in short supply nationwide.”

The percentage of the population taking cancer examinations stood in the 30 percent range to 40 percent range on average nationwide last year, far below the central government’s goal of 50 percent. Experts say reasons for the low rates is that taking a cancer examination can be complicated and that examinations are not offered at some areas.

“In the miRNA test, 13 types of cancers can be tested for at once and the one test only costs about ¥20,000,” Ochiya said. “We intend to speed up the process of putting the test into practical use.”

“It’s good news for people who possibly might be going to develop cancers,” said Kazuko Hamanaka, president of Cancer Patients Support Organization, a Tokyo-based nonprofit organization.

False positive results

However, there are some issues to be tackled for the miRNA method to be widely used.

Currently, the test method is thought to rarely miss cancers, but at the same time the test often gives “false positive” results, meaning a person may be thought to have cancer even if they do not. This is particularly problematic with breast cancer, for which about 20 percent of positive results were false positives, while the rates for the other 12 types were one-digit figures. This is because the researchers did not have access to enough stored blood from patients with noncancerous breast diseases for comparison, resulting in insufficient data.

“Further examinations [to confirm the presence of cancer] would be actually meaningless in 20 percent [of these cases], causing unnecessary worries,” Nakayama said. “The rate should be decreased to less than 5 percent [for the test] to be useful.”

As for cancers that develop fast, such as pancreatic cancer, it should be thoroughly discussed how frequently the test should be taken.

“Some early-stage cancers develop very slowly. Discovering such cancer in the early stages might lead to unnecessary treatment,” said medical oncology Prof. Noriyuki Katsumata at Nippon Medical School Musashi Kosugi Hospital in Kanagawa Prefecture. “Study should be conducted to check whether the introduction of the miRNA test will lead to a decline in the cancer death rate.”

■ microRNA (miRNA)

A molecular substance that controls the activity of genes in cells. So far, 2,588 human miRNAs have been found, and of them, about 500 kinds are believed to be covered in lipid substances and floating in blood. Types of miRNA differ between cancer cells and normal cells. Speech

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