Despite widespread belief to the contrary, as few as 6% of women experience cancer-related persistent fatigue a year after undergoing treatment for breast cancer, a new study has found.

Prolonged and disabling fatigue is a common side effect of many cancer treatments, with large numbers of women reporting that cancer-related fatigue persists for many months after treatment ends. Some studies put the figure as high as 50%.

But a study of breast cancer survivors from a group of collaborating hospitals in Sydney together with staff of the University of New South Wales’ newly established Cancer Survivors’ Centre has found that figure is overstated, with the previously reported high rates of fatigue most likely attributable to factors unrelated to the cancer or its treatment.

And while the study, published in the Journal of Clinical Oncology, looked at breast cancer, the researchers believe the same results would apply to survivors of other cancers.

"The good news is that the vast majority of women who have undergone cancer treatment either never experience ongoing debilitating fatigue in the weeks and months after treatment ends or if they do, it passes relatively quickly," said study author, Professor David Goldstein, from UNSW’s Prince of Wales Clinical School.

"This is not to say that cancer-related fatigue is not a problem. It is still one of the main symptoms of cancer and a major side effect of treatment, but people can be reassured that for the vast majority receiving adjuvant treatment, it is not an ongoing or long-term debilitating experience," Goldstein said.

The 5-year prospective study followed 218 women with early-stage breast cancer. The women were observed and questioned at 3-monthly intervals for a year after treatment and again at 5 years. A rigorous definition of fatigue was used to rule out any "background" fatigue.

The study found the case rate for cancer-related fatigue fell from 31% at the end of treatment to 11% at 6 months and 6% at 12 months.

The findings suggest that previous studies have overestimated the prevalence of cancer-related fatigue and included transient fatigue states associated with unrelated infections, surgery, minor psychiatric disorders, and chronic fatigue states attributable to other conditions.

The researchers say for the significant minority of people (6%) who do experience ongoing fatigue, attention can now be focused on early identification and directing resources where they are most needed.