Scientists are more certain than ever that Agent Orange is causing cancer in Vietnam War veterans.
A recent study of 479 Vietnam veterans who were involved in Agent Orange defoliation efforts in that country found that these individuals are twice as likely to develop a blood condition known as monoclonal gammopathy of undetermined significance, or MGUS. The disorder is a precursor for multiple myeloma, a type of blood cancer.
During the Vietnam War, Agent Orange was used by U.S. forces to kill off trees and vegetation in the jungles of Vietnam and Cambodia that the enemy used as cover. The chemical is composed of several herbicides – including 2,4-dichlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid – nicknamed for the orange stripe on the barrels in which they were stored. When these two herbicides are combined, they create a carcinogen dioxin known as TCDD, which is the most toxic of dioxins.
The U.S. Department of Veterans Affairs recognizes that Agent Orange causes multiple myeloma, several types of leukemia, and other cancers, as well as diabetes, heart disease, and Parkinson’s disease. Veterans are supposed to receive care for their medical problems if they can prove they were exposed to the chemical, and they can get disability compensation.
For the study, 479 Americans involved in Operation Ranch Hand spraying missions were compared to 479 veterans who were not. Dr. Ola Landgren of Memorial Sloan Kettering Cancer Center and colleagues found that 7% of Operation Ranch Hand vets had MGUS compared to only 3% of the other vets in the study.
“Our findings of increased MGUS risk among Ranch Hand veterans supports an association between Agent Orange exposure and multiple myeloma,” they wrote in the Journal of the American Medical Association’s JAMA Oncology.
“Most people who have MGUS will not develop multiple myeloma, but everyone who has myeloma first had MGUS,” Landgren said.
Approximately 30% of people with MGUS will go on to develop multiple myeloma within 30 years. Until now, there has been no scientific evidence that Agent Orange could cause the blood cancer. 
“It’s not proof, but it’s a good link to show there’s a connection,” said Dr. Nikhil Munshi, director of basic and correlative science at the Dana-Farber Cancer Institute’s Jerome Lipper Multiple Myeloma Center in Boston. Munshi wrote an accompanying editorial to the study, which was published online Sept. 3 in JAMA Oncology.
Landgren and Munshi recommend that veterans exposed to Agent Orange have their blood tested for signs of MGUS. If the disorder is detected, they will need to schedule regular follow-ups to make sure their MGUS doesn’t progress to multiple myeloma.
 NBC News