Breast cancer rates among pregnant women are on the increase because would-be parents are waiting longer to have children, an expert has warned.
The diagnosis of the disease in expectant mothers leads to a terrible dilemma as the treatment can be devastating for the unborn child.
But despite this doctors now believe the treatment should remain the same as women without cancer.
Their treatment should follow that of a non-pregnant woman as "closely as possible", say researchers, although in collaboration with specialists including an obstetrician.
But the chances of birth defects in children were higher amongst breast cancer patients regardless of what treatment they received, the team found.
The study looked at 313 pregnant women with breast cancer to see how their treatment affected the child.
Presenting the findings at the San Antonio Breast Cancer Symposium, lead researcher Dr Sibylle Loibl said that although it was uncommon for breast cancer patients to be pregnant – between two and three per cent – as women delay having children until later it may become more widespread.
Dr Loibl, of the German Breast Group, said: "At the time we started the study in 2003, there was hardly any information on breast cancer therapy during pregnancy, but we felt there was a medical need for it."
The seven year study looked at women aged between 23 and 47, with various types of cancer in different stages.
Of the women, 23 per cent were in their first trimester, 42 per cent in the second and 36 per cent in the third.
Various treatments including chemotherapy were used to treat them.
Two of the infants died shortly after birth, and 29 of the women did not continue the pregnancy. Premature babies were found to be more common among those who did not receive chemotherapy, and the children of those who did tended to weigh a little more.
The children of both groups were found to be at higher risk of congenital problems than the usual population.
Infants from both groups experienced congenital problems, most of which were related to premature birth.
Dr Loibl said: "We were surprised about the number of congenital malformations. It is about 1 to 3 per cent in the general population, but was higher in this cohort."
The average survival time for the women was 55 months.
Dr Loibl said the research meant she would advise her pregnant cancer patients to "continue the pregnancy and start with a treatment as closely as possible to standard recommendations for nonpregnant women".
She added that it was "critical" that a multidisciplinary team in close collaboration with an obstetrician, prenatal care specialist and a neonatologist treat the pregnant woman with breast cancer.