More bad news on the prostate cancer front: A widely used test that’s supposed to help doctors and patients predict the outcome of most prostate cancers is basically worthless.

That’s according to a study just published in the journal CANCER.

The new study discrediting the test, coupled with persistent questions about how useful prostate screening is for most men anyway, add up to a whole lot of discussion points patients should take to their doctors.

The test in question is called “clinical staging.” It relies on certain signs doctors use to classify how advanced an individual patient’s cancer is – that is, what stage it’s in. It includes criteria like whether the doctor can feel a nodule through rectal examination, and whether a tumor is detected through a test called trans-rectal ultrasound.

Ten years ago, the American College of Surgeons Commission on Cancer decreed that doctors should use these types of clinical staging tests to help decide how to treat cancers.

“Our findings question the utility of our current staging system for localized prostate cancer,” says Dr. Adam Reese of the University of California at San Francisco, lead author of the study.

To begin with, doctors err in using this prostate test 35 percent of the time. When these errors occur, the study says, doctors most often conclude the cancer is less serious than it really is.

But even when researchers allowed for these errors, they found the test doesn’t predict how patients ultimately do.

Dr. Gerald Andriole of Washington University, who was not involved in the study, told Shots he wasn’t surprised by the results. Recently, he says, urologists “have begun to realize these criteria are not adequate. But this is the first study that quantifies the magnitude of the inadequacy.”

Even so, Andriole says, the findings may not make too much difference in the real world. Before treatment recommendations are made, doctors put most prostate tumors through other tests, too, like the Gleason score, and they look at the percentage of biopsies that are positive for cancer cells.

“I use all those parameters to tell a patient what his chances of a good outcome are,” Andriole says.

Still, both study author Reese and Andriole say the new study may serve as a wakeup call to those who are over-relying on the clinical staging system.

They say what’s really needed is a set of tests that classify prostate tumors by what genes are turned on or off in the cells.

Once this is sorted out, doctors treating prostate cancer will be less like the blind men who try to guess what kind of creature they’re dealing with when they grasp the elephant’s trunk or tail.