Urgent, doctors :' (my mom has metastases liver cancer, lung and bone nearby left thigh found tumors. Just found out few days ago, is stage 4. How?

This is too. Common. Some cancers are quiet until they infest other organs, and it is these organs working poorly or hurting that causes the cancer to be known. Some cancers can have life extended by treatment (prostate and breast), others can be treated to relieve symptoms. But for most, it means time to focus on comfort and symptom relief rather than rigorous treatment.
Unfortunate. I am sorry to hear about your mother. Unfortunately, cancers can spread and many times rapidly. Ideally, cancers are found early before they spread, but unfortunately, many times symptoms don't develop until it does.
Yes. Unfortunate, but true. Cancer cells found any place other than the 'point of origin' makes it 'metastatic' and by established norms in tnm classification system, acquires a late stage...