Treating cancer has advanced significantly as routine screening for certain forms of the disease has increased.

So, too, has the debate over when and how to test for it.

On Wednesday, researchers will unveil three large studies on efforts to screen for several types of cancer, allowing for a better understanding of how to detect the diseases at their critical beginning stages. Catching the disease before it spreads to other parts of the body usually improves treatment success.

However, while screening has evolved, questions remain about the stress of overtesting and excessive treatment in some cancers.

“If we look at overall cancer mortality, which has been decreasing since the early 1990s, a large part of that has been attributed to cancer-screening activities,” said Therese Bevers, medical director of the cancer prevention center at the University of Texas’s M.D. Anderson Cancer Center.

The data will come as the American Society of Clinical Oncology publishes more than 4,000 cancer-related clinical studies Wednesday, ahead of its annual meeting in early June.

ASCO will detail the results of a study assessing whether prostate-specific antigen, better known as PSA, levels in a group of Swedish men aged 44 to 50 can predict the risk of the cancer spreading or the patient dying up to 30 years later.

Another study will show whether the blood levels of a protein call CA-125 and use of a type of ultrasound can detect early ovarian cancer, a disease that has no standard screening. A third study will examine the effectiveness of testing for human papillomavirus alone or in combination with a Pap smear in identifying those women with a high risk for cervical cancer.

Screening is done in people with no symptoms to find a disease at its earliest stage, as opposed to diagnosing a known problem.

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