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.

Past studies have often been "cross-sectional," meaning they studied people at one time-point.

So it's possible to catch some bouts of fatigue that are related to various causes, explained Dr. David Goldstein, who led the new study.

That could mean lingering fatigue from a viral illness, for example, or fatigue related to depression, according to Goldstein, of Prince of Wales Hospital in Randwick, Australia.

"There are cancer survivors with true post-cancer fatigue," Goldstein said in an email. It's just that the number may be "less than previously thought."

That may be true at least with early-stage breast cancer -- and possibly some other early cancers, Goldstein said -- but not necessarily more-advanced cancer.

"The fatigue associated with advanced cancer is a much more complex issue -- tied up with the biology of an active tumor and its many physical effects, as well as the drugs used (for treatment)," Goldstein explained.

The findings are based on 218 women who were treated for early-stage breast cancer with surgery and some type of "adjuvant" therapy, usually radiation, chemotherapy or both.

The women answered questions about their physical and psychological health every few months for a year after treatment. Overall, Goldstein's team found, 11 percent persistently had fatigue at the six-month mark, while six percent still had symptoms a year after treatment ended.

Goldstein said the study used a questionnaire that distinguished between physical and psychological symptoms, which some past studies have not done. And women who had persistent fatigue at six months were evaluated to rule out "alternative" causes -- like low thyroid hormone levels or depression.

It's not clear why some women treated for early breast cancer remain fatigued for months or longer, according to Goldstein.

Some recent research, he noted, has hinted that some patients could have a genetic predisposition to an "exaggerated bodily response" to chemotherapy, for example.

Other work has suggested that chronic, body-wide inflammation could play a role.

As for fatigue treatment, there's evidence that good sleep habits and regular exercise can help, if people can keep those habits up.

Based on research into chronic fatigue, a combination of exercise plus cognitive behavioral therapy might help some patients, according to Goldstein. He said he and his colleagues are currently studying that approach.

Cognitive behavioral therapy is a form of talk therapy focused on changing the thought patterns and behaviors that seem to be feeding physical or mental symptoms.

One recent study also found that breast cancer survivors who got more omega-3 fats in their diets were less likely to have long-lasting fatigue than survivors who ate less. (See Reuters Health story of March 29, 2012)

Omega-3 fats, which are thought to fight inflammation, are largely found in oily fish like salmon, mackerel and tuna.

Those findings, though, do not prove that omega-3 directly affects the long-term risk of fatigue. And the researchers said it was too soon for cancer survivors to be taking fish oil to battle fatigue.

They noted, though, that eating fish a couple times a week -- something that's already recommended for general health -- could be a good idea.

SOURCE: bit.ly/I6BRhd Journal of Clinical Oncology, online April 16, 2012.

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