Do you have any experience with unexplained weight loss?
No, is it a health challenge? 
No, unexplained weight loss is not caused by dieting, but can be a symptom of a serious medical condition.
You mean one would just loose weight simply by starving  his or herself? 
no it usually happens when someone is sick - like cancer - it happens when the body is expending more energy in work than absorbing in food.
So are there  treatment of such cases? 
It depends on what the underlying cause is, while these symptoms may indicate cancer, they may also have other causes.