A significant weight loss always raises the possibility of malignancy. In this case, the patient has had poor appetite and diarrhea as possible causes of the weight loss, but you should keep the possibility of a tumor in the back of your mind whenever you see a history of major weight loss.
Amenorrhea can be associated with chronic disease and weight loss. It could also signal an endocrine-related problem.
In general, these symptoms could be produced by a number of chronic inflammatory diseases or GI-related problems. However, the finding of a diffusely-enlarged thyroid indicates that endocrine-related disease should be evaluated in the initial laboratory testing.