Did my hamster menstruate?

Last night my hamster, Gizmo, was bleeding. Not much, mind you. There were a couple tiny spots of blood on her bedding, a couple small spots on me from picking her up, and some smeared in her, umm, “crotch,” if you can call it that on a hamster. She had zero other symptoms at the time (she was as active as usual, she ate fine, etc.). Today she is blood- and symptom-free. Gizmo is about 21 months old.

Given that information, what are some possible causes of her bleeding? My first thought was “Woah, I didn’t know hamsters had periods!” Do they? I’ve had several hamsters over the years, and this would be a first (unless I’ve just not paid attention all this time). I assume things like cancer and digestive maladies are possibilities, but I really don’t know how those things manifest themselves in hamsters.

Any thoughts?

Found this, FWIW.

http://experts.about.com/q/2005/3063344.htm