Cancer of unknown primary! whst treatmens and how successful are they.

oncology handed down a verdict of stage four cancer. they know its cancer and where it is , but not what kind or where it started. The cancer so far doesn't seem to be in the organs but wide spread in soft tissue. Radiation treatments start this week and it will take two weeks for genetic testing to find out what kind it is. How can they determine that it is all the same type and if it will respond to treatment the same way.