In my book, Deformed and Destructive Beings: the Purpose of Horror Films, I talk about how appearances in horror films affect actors' careers. The movie Case 39 (2009) is a case in point.
For those who missed it--probably many--Case 39 is an evil child horror movie, in the tradition of The Bad Seed and The Omen. All you need to make this type of film is a cute, wide-eyed, innocent-looking child who, when properly lit and coached, can look like the spawn of Satan (literally so in the case of The Omen). In Case 39, the child, Lilith (played by Jodelle Ferland), is apparently abused by her parents, so much so that when the social worker, Emily (Renee Zellweger), shows up one night, the parents are busy stuffing young Lilith into the oven, taping the oven shut, and setting it to bake. This does seem like a terrible thing to do to somebody, especially one's child, so Emily gets the parents arrested and takes Lilith home with her. This is where the trouble begins.
As cute as Lilith is, it turns out that she can force people to have terrible hallucinations that drive them to kill themselves, and is just generally, well, a bad seed. Zellweger figures out that Lilith is some sort of demon that does need to be destroyed, perhaps not in an oven but maybe in a car...in a lake.
The movie is not a great horror film, though the good performances of Zellweger and Ferland boost it above the level of pure retread. What is most interesting is where it stands in Zellweger's career. Many are the actors who get their start doing horror films; a few advance beyond this level to become stars; and then some of these stars go back to doing horror films on the way down. This is Zellweger's fate. She started off appearing in Texas Chainsaw Massacre: The Next Generation (1994), got her big break opposite Tom Cruise in Jerry Maguire (1996), and went on to several strong starring vehicles such as Bridget Jones's Diary (2001). But by 2009, when Case 39 was released, she was not doing so well. It was the year she turned forty, good roles were hard to get, and so she appeared in Case 39. Her career has not yet recovered, though you never know what will happen next in Hollywood.
Just to show the symmetry of this, Bradley Cooper, who supported Zellweger in Case 39 as her boyfriend, was moving in the opposite direction at that point. He had already made a horror movie, The Midnight Meat Train (2008), and now was appearing in another one--Case 39. That same year, The Hangover (2009) was released--which was Cooper's big break. Since then his star has been rising, all the way to an Oscar nomination for best actor in American Sniper (2014).
It appears that horror films can be helpful to an actor's career, especially in the beginning, but can spell trouble later on. Aging can also be a problem, especially for women: Zellweger is six years older than Cooper. At least horror film fans are loyal. When other options are gone, there's always horror.