COLUMBUS, Ohio, May 6 (UPI) -- Past mood/anxiety disorders put cancer patients at risk of post-traumatic stress disorder, or PTSD, a U.S. study says.

Study co-author Barbara Andersen of Ohio State University says the findings show the majority of breast cancer patients are not at risk for PTSD. However, doctors should screen newly diagnosed breast cancer patients for past mood disorders and anxiety disorders.

The study, published in the Journal of Traumatic Stress, of 74 breast cancer patients at the Ohio State University Medical Center, found 12 women, or 16 percent, suffered from PTSD 18 months after diagnosis.

The study shows breast cancer patients with PTSD are more than twice as likely as breast cancer patients without the disorder to have suffered from previous mood disorders -- such as depression -- and more than three times more likely to have experienced anxiety disorders before the diagnosis of cancer.

"What is unique about breast cancer patients with PTSD is that they have already had this double hit of both anxiety and mood disorders even before they got the diagnosis," Andersen says in a statement. "So when they are in a new situation that is very anxiety provoking -- cancer diagnosis and treatment -- it is not surprising that they are at risk for developing PTSD."