Can physician assistants specialize in anything?

Yes: Physician assistants (pa's) can have special knowledge in certain areas, such as pediatrics, surgery, obstetrics, etc... Their specialization is usually due to working in the particular specialty for several years. Some pa schools may have programs to help pa's specialize. Licensing rules vary from state to state, so there may or may not be state recognition of any specialized pa's.

Yes: PAs in some areas become quite skilled in a limited discipline. For instance a number of cancer treatment centers use physician assistants to handle all the routine aspects of treatment for cancer patients. They become in this setting, true specialists.