Here are some of the latest health and medical news developments, compiled by the editors of HealthDay:

Some Young People With STDs Say They've Never Had Sex: Study

Ten percent of young adults who tested positive for one of three common sexually transmitted diseases (STDs) said they hadn't had sex in the previous year, including six percent who said they never had sex, finds a new study.

The researchers said their findings from 14,000 participants who were screened for chlamydia, gonorrhea, and trichomoniasis held even after they factored in variables such as race, age, gender and education, the Washington Post reported.

The study was published in the journal Pediatrics.

The researchers said their findings suggest that doctors should use lab tests to screen all teens and young adults for STDs, instead of focusing only on those who admit to being sexually active, the Post reported.

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New Blood Test Could Improve Cancer Patients' Care

Scientists say they've developed a highly-sensitive blood test for cancer that could lead to major improvements in patient care.

The new test can detect a single cancer cell among a billion healthy cells, according to the Boston scientists who invented the test. They'll team with Johnson & Johnson to bring the test to market, and four major cancer centers will launch trials of the test this year, the Associated Press reported.

Cancer cells in the blood indicate that a tumor has spread or is about to do so. Being able to capture and analyze these cells can help doctors determine the best treatment approach and monitor the effectiveness of treatments. The new test may also prove useful in cancer screening.

Currently, the only available test to find tumor cells in the blood just gives a cell count, the AP reported.

"There's a lot of potential here, and that's why there's a lot of excitement," Dr. Mark Kris, lung cancer chief at Memorial Sloan-Kettering Cancer Center in New York City, told the AP. He was not involved in the development of the new blood test, but Sloan-Kettering is one of the sites that will assess it.

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Exercise Tied to Lower Risk of Colon Cancer Death: Study

Exercise may decrease your risk of dying from colon cancer, according to a new study.

U.S. researchers analyzed physical activity levels and colon cancer deaths among more than 150,000 women and men and found that those who exercised consistently for at least 10 years were least likely to die from colon cancer, United Press International reported.

The study appears in the journal Cancer Epidemiology.

Many people wonder whether exercise will help them stay healthy, said researcher Kathleen Wolin, of the Siteman Cancer Center at Washington University School of Medicine and Barnes-Jewish Hospital in St. Louis.

"It's never too late to start exercising, but it's also never too early to start being active," she said in a news release, UPI reported.

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