cancer?

My husband has these syptoms weight loss, constant heart burn, nausea, dark stool,flu like syptoms,

Such cluster of symptoms certainly needs to be evaluated by a doctor as it could be indicating many diseases and problems.
Although early cancer goes without symptoms, some of the most common cancer symptoms would be: a lump, a change in a mole or a wart, sores that do not heal, prolonged coughs, chronic fatigue, bowel habit changes, problems with indigestion, strange bleedings etc but such symptoms could be indicating a whole range of other problems.
There are tests that can easily detect cancer and some of them are anti-malignin antibody screen test that is used to detect advanced cancers before other conventional medical tests. Then there are cancer marker tests used to detect markers produced by growing cancers. Then there are tests that will show how healthy your cells are by measuring your blood, saliva and urine in order to check the amount of electrons present, pH balance, and minerals in these fluids. It is called Biological Terraine Assessment (BTA).
The thing is that nothing can be said without seeing a doctor and symptoms alone are not a good indicator except for ordering tests. Your husband must undergo tests in order to find out what is going on.