The study by Norwegian scientists has found that for almost all types of cancer, the survival of women who are diagnosed during pregnancy or who became pregnant after being treated for the disease is no different from that of other female cancer patients.
"The only exception was for breast cancer diagnosed during lactation, where women were 1.9 times more likely than normal to die from their cancer," said Dr Hanne Stensheim, a research fellow at the Norwegian Cancer Registry in Oslo, Norway, who led the study.
"We think this is mainly based on greater delay in diagnosis, rather than any influence of the lactation process itself. It may be more difficult to diagnose breast cancer during lactation because many women get lumps due to mastitis and because normal physiological changes in the breast might mask suspicious developments,' Dr Stensheim added.
In the study, the scientists tracked the cancer of 45,511 women for an average of eight years and compared the survival rates of patients who did not get pregnant with those of patients who either were diagnosed during the gestation or lactation period, or who got pregnant after cancer diagnosis and treatment.
"Many women are concerned about pregnancy after cancer, as are many doctors. There have been several hypotheses for decades proposing that complex hormonal changes and immunologic alterations associated with pregnancy might promote cancer growth," Dr Stensheim said.
"Those studies that confirm such hypotheses are often based on small numbers and the findings could be due to selection bias. I see our results as further reassurance that pregnancy factors are not influencing the cancer development per se," he added.
While previous studies on cancer during pregnancy tended to investigate a single cancer type and draw information from a single institution, the latest study is population-based and includes all cancer types found in Norwegian women diagnosed between 1967 and 2004 and is thus among the broadest studies of its type to date.
"With adjustments for age, stage and diagnostic period, we found no significant difference in survival for pregnant women diagnosed with a malignancy compared to non-pregnant cancer-patients," Stensheim said.
"I think this might justify the statement that pregnancy does not affect the clinical final outcome of a malignant disease in general," he added.