My little brother had his cancerous tumor removed yesterday.
My younger brother had a surgery to have his tumor removed yesterday.
My younger brother had surgery to remove a tumor yesterday.
I'm glad (that) it was a great success!
Remove a tumor は「腫瘍を除去する」という意味です。がんは英語でcancerですけど、同じ文章であまり言わないです。普段は別の文章を言います。例えば、My younger brother has cancer, but he had the tumor removed yesterday.
「~て良かった」は英語で I'm glad (that) です。Thatは使わなくても構いません。例えば、I'm glad you made it on time. または I'm glad that you got the job!