Does the doctor need to do to tests to be sure if the diagnosis is bone metastases?

Usually: Bone metastases are where cancer from one site (breast, prostate, lung) spreads through the blood and begins to grow in the bone. This can have a characteristic appearance on scans. The way to prove it is cancer is to take a biopsy. However, if cancer has already been diagnosed, bone metastases can be diagnosed by a characteristic bone scan or other radiographic test.

Sometimes: In many cases, it is not necessary because there is established progressed cancer and this is another manifestation, but if there is one lesion, no prior record of metastasis, it is quite reasonable to biopsy to prove metastasis.