Is It Safe To Take Progyluton?

hi,i'm 23 yrs old,unmarried.i have this problem of unequal breast,which is my right breast is smaller than my left.my doctor assessed it for any lumps or nodules but he said it's still developing.he advised me to gain weight because i'm 43kg. and prescribed progyluton to help the size increase of my breast.is it ok to take this pills?and also,i'm afraid about rumors that taking pills can be a cause of having cancer in the future.hoping for your reply. tnx.