Elizabeth Edwards has been told the metastatic cancer found in her bones is considered stage four. And it's treatable. But not curable.

Tricky stuff -- all this cancer terminology -- and a little hard to fully comprehend.

I saw Sheryl Crow talking with Maria Shriver and Dr. Susan Love on Larry's King's CNN program the other night. Crow says her breast cancer was curable -- it was teeny tiny and had not spread and required a lumpectomy and radiation, but not chemotherapy. "I'm the walking poster child for early detection," she said. Her cancer was caught and treated swiftly. She is cured. Theoretically.

Can Crow's cancer still return? Yep.

We just aren't sure at the time of one cancer discovery if these deadly cells have drifted away from the main site and will later show up elsewhere, explained Dr. Love. All predictions would have Crow living a long life free of cancer. But they may have had Edwards in the same boat just two years ago when she was first diagnosed with breast cancer.

So now Edwards' cancer is not curable. It is treatable. And this is a bit easier to understand. Her cancer will never go away. But doctors can keep it at bay. And Love says they can even make it better. But there is no cure for what Edwards has. So she will live with cancer for the rest of her life.

I guess curable means: the cancer is gone and we hope it never comes back. And treatable means: the cancer is not gone and will never be gone but we will treat it for as long as we can.

I think I get it.

Researchers at the Marie Curie Institute have said that they now understand how melanoma spreads to other parts of the body. They feel that this information can help in uncovering how other cancers metastasize.

A gene called MITF controls a switching mechanism inside the malignant cell. It seems that MITF levels determine whether the cell is dividing, proliferating, forming a tumor, or whether it goes into a non-dividing state, which becomes highly invasive. The researchers were surprised and assumed that the dividing cells would become invasive.

Chemotherapy goes after dividing cells so researchers think that these non-dividing cells are the dangerous ones that lead to metastasis to other organs.

In a feature published in the Sydney Morning Herald, Julietta Jameson asks the same question many of us have asked -- Is the compassionate celebrity the new public pest? If you are talking about Paris Hilton's insatiable self-promotion in grabbing one more photo-op by making a shallow meaningless promise to a charity for kids with cancer, the answer is a resounding yes. If you are talking about U2's Bono, who regularly meets with world leaders and often knows far more about the subject under discussion than the politicians do, then the answer is an emphatic no.

Then there are all the celebrities who fall between the extremes of Hilton and Bono, who lend their name and some of their time, for noble reasons and then too for the less-admirable ambition of keeping themselves in the news, to causes that need attention for the fundraising needed to keep the charity or cause going.