Not the happiest subject you'll talk about today, but probably the most important. Some estimates say up to one out of every two people will get cancer at some point in their lives. Here are four important early warning signs to watch out for.

1.  Unexplained weight loss.  Sudden weight loss when you're not on a diet is one of the most common early signs of cancer.  It's most likely to occur with cancers of the stomach, pancreas, esophagus, or lung.  It could also mean diabetes, or liver disease.

2.  Persistent low-grade fever.  This is common with leukemia and lymphatic cancers.  We're talking about fevers between 99.8 and 100.8 degrees.  These would also be caused by different kinds of infections, but either way you shouldn't ignore them.

3.  Worsening fatigue.  If you're suffering from extreme fatigue, like the kind where you're sleeping three or four hours in the middle of every day, this could be a sign of cancer.  Leukemia, colon cancer, and stomach cancer could be likely causes.

4.  Skin changes, or sores that won't heal.  Everyone knows to watch out for irregular moles, or moles that change size.  But persistent sores can also be signs of cancer . . . not necessarily skin cancer.  Lung cancer and colon cancer can cause these too.

(Yahoo! Health)