Pregnancy may be the worst time for a woman to discover she has breast cancer because the pregnancy complicates treatment.

However, previous studies suggesting that breast cancer during pregnancy makes the disease more aggressive and more likely to return are being contradicted by new research from the University of Texas M. D. Anderson Cancer Center.

"There was always the concern that patients with breast cancer would have a more aggressive form of breast cancer, or have a worse prognosis, because of their pregnancy,” said Dr. Laurie Kirstein, a breast surgeon at the Texas center.

Researchers at M. D. Anderson found that pregnant women who develop breast cancer have the same survival rate and the same risk of the cancer's returning as other women.

The earlier studies had linked the gloomier prognoses to hormone levels during pregnancy.

What remains the same is that pregnancy makes finding and treating breast cancer more complicated because radiation and most chemotherapies are dangerous to the fetus.

"You can do surgery, and there are certain chemotherapies that we have found to be safe, at least during the second and third trimesters of pregnancy,” Kirstein said.

While mammograms can't be used, ultrasounds are an effective tool to spot breast cancer tumors. But the study found that tumors discovered in pregnant patients were often more advanced.

"Sometimes people, patients or doctors, may think that a lump in the breast is due to the pregnancy itself and they don't get a workup of the lump that they find,” Kirstein said.

Kirstein stressed that pregnant women should continue self-breast exams and be aware of any changes in their breasts.