Experts say they have found, for the first time, that it is safe for women with the most common form of breast cancer to become pregnant.
Those diagnosed with oestrogen receptor positive breast cancer – which accounts for 80 per cent of cases – can become pregnant without worrying it will increase their chances of the disease returning.
Previously, doctors feared that pregnancy could boost levels of oestrogen and cause the cancer to recur.
The findings, presented at the European Breast Cancer Conference in Vienna, suggest it is safe for women to become pregnant even within two years of diagnosis.
The study also found that patients who become pregnant appear to survive longer than those who do not, although further research is needed in this area.
Oestrogen is a female sex hormone which stimulates some breast cancers to grow by triggering particular proteins (receptors) in cancer cells.
In a previous study, Dr Hatem Azim Jr and colleagues performed a review of 14 trials which showed it was safe for breast cancer patients to conceive.
However, the study was unable to show whether this was the case for women with oestrogen receptor positive (also known as ER+) disease.
In the new research, Dr Azim, a medical oncologist at the Jules Bordet Institute in Brussels, and colleagues, enrolled 333 women whose oestrogen receptor status (positive or negative) and disease outcome were known.
Dr Azim said the study shows “convincingly that pregnancy any time following breast cancer diagnosis is safe.”