Welcome to Connect @babii. As an aggressive leukemia survivor, I can tell you that survivability rates can be misleading. So much is dependent on the source of the information and on the patient’s personal health condition, the phase of the disease, whether there are co-morbidities and the like.
I know you’re trying to find out information for your brother. The internet, while it can be helpful, can also lead us to information that causes undue stress. Some of it may not even relate to your bother. Your brother’s hematologist oncologist will discuss this with him and come up with a viable treatment plan.

There has been some postive treatments for CML developed over the past few years. From articles that I’m reading, the news is very encouraging. Here are two from credible sources that virtually say the same thing.

This article by Healthline.com: “The percentage of people living five years after a CML diagnosis who are treated with imatinib is 90 percent.” https://www.healthline.com/health/chronic-myelogenous-leukemia-cml
~~~~
Another article, this one from American Cancer Society:
“One large study of CML patients treated with imatinib (Gleevec®) found that about 90% of them were still alive 5 years after starting treatment. Most of these patients had normal white blood cells and chromosome studies after 5 years on the drug.” https://www.cancer.org/cancer/types/chronic-myeloid-leukemia/detection-diagnosis-staging/survival-rates.html

Was your brother just diagnosed? Has he had a treatment plan discussion yet?

Hi: CML is very treatable. I was diagnosed in 1998, and there were no TKI drugs to treat it. I was told 6 months to a year without a bone marrow transplant. I was 52, and I am now 76 going on 77. I have been undetectable after taking Gleevec (Imatinib) for 18 years. I did the clinical trial for the Gleevec back in 2000. Prior to getting into the trial, all they could offer me was some heavy duty treatment that did not work for me. I am in a deep remission, and been off all treatment for 6 years. I do have to be checked constantly to be sure I am holding the remission. I am sure that your brother is or will be put on a what we call a TKI drug. There are various drugs and they just have to find which one will work for him Please keep us updated as to his progress. Tell him to stay positive, because he can beat this.