Many of the top schools don’t have Communications or Marketing majors, considering them more pre-professional than academic.
Students at top schools who want to go into these areas study a variety of different fields: literature, journalism, business, finance, economics, etc. and try to forge industry connections through summer internships.
In the US, many people in PR and corporate communications are former journalists, who have very strong writing skills and understand the way media works. But again, many top schools don’t have undergrad journalism majors, and those that do (Northwestern is a good example) are very, very competitive.