The VA has an overview of the research:
http://www.publichealth.va.gov/exposures/agentorange/researc...
Interesting! Of course, the VA would have followed up. A quick perusal of the papers seems to indicate that the connection between AO and cancer are "non-significant" at least in the studies done so far.
Little difference in risk, however, was noted according to dates of service, type of unit, military region, or any other characteristics that may have been associated with the use of Agent Orange.
Birth defects happen even when no one is exposed to Agent Orange. Without a study, you wouldn't be able to determine how many more birth defects happened.