Why does the incidence of breast cancer increase among pregnant women?

Mats Lambe answers five questions concerning breast cancer and pregnant and breast-feeding women.

Pofessor Mats Lambe. Photo: Ulf Sirborn

Text: Cecilia Odlind. Published in the magazine Medicinsk Vetenskap nr 2 2010.

Breast cancer that arises in association with pregnancy has increased – why is this?
"The increase can be attributed to the fact that more women are delaying starting a family, when the risk of being affected by breast cancer is higher."

Does the risk of being affected by breast cancer increase during pregnancy or breast-feeding?
"There is no clear evidence that the underlying risk is higher: it is probable that the tumours that are detected during pregnancy or immediately afterwards have been there for some time before the woman became pregnant. What may be happening, on the other hand, is that the growth of pregnancy-associated tumours is influenced by the high hormone levels or by other changes that take place during pregnancy and breast-feeding."

Research has also shown that the diagnosis of breast cancer in pregnant and breast-feeding women is often delayed. Why is this?
"One probable reason is that the symptoms and changes that arise are interpreted as being caused by the pregnancy itself. Furthermore, the diagnosis is made more difficult by changes that the breast glands undergo."

What can the healthcare services do?
"It is important to raise awareness of pregnancy-associated breast cancer, both within the health and medical care services and among women of childbearing age. Only then will the disease receive the early attention required. A delayed diagnosis means delayed treatment, and this can lead to a poorer prognosis."

Does pregnancy affect the prognosis?
"Some results suggest that women with pregnancy-associated breast cancer have a poorer prognosis than women of corresponding age with breast cancer that has arisen without being associated with pregnancy. This is one of the questions that we are studying in a research project."