The Latino Review is has released a report listing several characters from the Marvel Cinematic Universe that may be making an appearance in Ant-Man.
The report is unconfirmed and should be considered a rumor at this point. (so take it with a grain of salt)
Potential SPOILERS to follow.
The Latino Review states that Edgar Wright's original script for the film featured a prologue scene that focused on the original Ant-Man, Hank Pym.
According to the report, this scene would include appearances by several characters from the early era of the Marvel Cinematic Universe, including Agent Peggy Carter, Howard Stark, Arnim Zola, and a young Alexander Pierce.
While they can't confirm this for certain, the Latino Review wagers that the scene survived the script rewrites that followed Wright's departure from the film, largely because it's a strong scene, but also because it serves as a nice film tie-in to the upcoming Agent Carter television series.
Ant-Man will come to theaters July 17, 2015.