The study, of 218 women treated for early breast cancer, found that almost one-third had "cancer-related fatigue" at the end of treatment. But far fewer -- six percent -- still had the problem a year later.

That suggests for most women with the disease post-treatment fatigue will fade with some time, the researchers report in the Journal of Clinical Oncology.

It's well known that cancer patients often suffer fatigue. And some studies have concluded it's common for that weariness to last for years after treatment ends. Among breast cancer survivors, researchers have found that more than one-third have fatigue two to three years after treatment.

The reasons, though, have not been clear. And the new findings support the idea that some cases of chronic fatigue in earlier studies may have had causes other than the cancer itself.