My mom's right breast keep "beating". 2 last year doctor said she got cancer, and last year the cancer is smaller. is it dangerous? thanks

Unsure....: When you say 'beating' i assume you're feeling a pulse = her heartbeat. That has nothing to do with cancer; if heartbeat is stronger or harder, see doctor. A cancer should have been surgically removed; as a result, I am not sure what is meant by the 'cancer is smaller'; perhaps you are referring to spread of the cancer to another organ? Please re-ask your question so i can help you better.

Cancer is dangerous: Sorry but i'm not sure what you mean by "beating". Perhaps you're referring to an aneurysm? Regardless, it needs to be evaluated. So last year, she was diagnosed w/cancer (where?) and it was smaller? Well, untreated cancers typically grow. Which is why she needs to be evaluated & offered appropriate treatment (or hospice if she would prefer no treatment & is ready to accept death).