Long-term cancer prognoses cannot be made with any precision. By looking at statistics you have already lost sight of the fact that some people survive this cancer with complete remission. There's no way to predict which people will beat the odds.
Any secondary cancer has a poor prognosis because if its in one place, its likely to be in another, and it means the cancer cells have a lower likelihood of responding to treatments. Anything can happen from a rapid deterioration to complete remission, with an unfavorable outcome being more likely - this is the most accurate prognosis since it includes the entire range of possible outcomes.
The previous response about esophageal cancer stage 4 might be what a registrar uses to record this cancer in the books, but from a treatment perspective its osteosarcoma, which is obviously treatable.