That works only in a specific context.
e.g.
昨日の地震で、佐藤さんは、お母さんがけがをしました。前田さんは、お父さんが亡くなりました。
There's a well-known sentence 僕はウナギだ. This doesn't mean "I'm an eel" in a fairy tale or something (yes, it can mean so, of course). A famous linguist 奥津敬一郎 gave this example to explain the function of は. He said that this is commonly used in a conversation as "unadon (bowl of eel and rice ) please" when ordering dishes in a restaurant. It's naturally interpreted as 僕はウナギを注文します from the context. Similarly, 佐藤さんは and 前田さんは means 佐藤さんについては and 前田さんについては in the sentence above, respectively.