Women diagnosed with ductal carcinoma in situ, an early form of breast cancer, tend to overestimate their risk of recurrence, even though the prognosis is good, researchers say.

In DCIS, the cells lining the milk ducts in certain areas of the breast are cancerous, but stay within the ducts without getting into the breast tissue.

According to the study, published online Tuesday in the Journal of the National Cancer Institute, the risk of cancer spreading elsewhere in the body is one per cent. If a mastectomy is performed, the likelihood the disease will return is one per cent, and it is under 10 per cent in cases where the lump has been removed but the breast has been preserved.

Despite the prognosis, many women are anxious about the cancer's return, the study suggests. 

Researchers who interviewed 764 women to measure their perceptions of DCIS found more than half of the 487 respondents said they believed they had a "moderate likelihood" of their cancer returning within five years of receiving their diagnosis.

Sixty-eight per cent believed DCIS was likely to recur in their lifetime and 28 per cent thought that it was moderately likely DCIS would spread to another part of their body.

"This exaggerated sense of risk needs to be addressed, as it may cause women to make poor treatment choices, and adversely affect their emotional well-being and subsequent health behaviours," said Ann Partridge, the study's lead author and a breast oncologist at Dana-Farber Cancer Institute in Boston, in a release.

The women were interviewed immediately following diagnosis, at nine months and 18 months. Their perceptions remained much the same during the study period.

Women who were generally more anxious before the diagnosis were more likely to believe their DCIS would recur within five years or that it would develop into invasive breast cancer within five years or during their lifetime.

The authors are not sure whether the anxiety is caused a false set of risks presented to the patient or whether their perceptions stem from their anxiety.

"Some of the anxiety is clearly tied to our society's fears about breast cancer," said Partridge. "A woman may also have multiple care providers — medical oncologist, surgeon, plastic surgeon, internist — and may hear mixed messages about her risks.

"Improved understanding of DCIS on the part of the medical community may also help women make better, more informed decisions about their care."