Hi, thanks for posting your query
The treatment you are being given is apt for melasma
. Topical steroids
are not known to cause cancer , so dont worry but they can cause skin atrophy, visible blood vessels ,hypopigmentation
The cream which you are using might be having moderate steroid momatosone or a milder hydrocortisone
which may cause above mentiond side effects if used for a longer time , so you may discuss it with your treating doctor.
Hope this solves your query