Israeli researchers have suggested that women who have a positive outlook on life may decrease their chances of developing breast cancer by maintaining the same attitude.

Another study also found that getting divorced, being bereaved or going through at least one traumatic event in your life could increase that risk. The only trouble with these researches is that the women were questioned following their diagnosis, which could have significantly changed their outlook on life.

So, the role of mental outlook on cancer remains controversial, with some studies suggesting that it might play a role and others denying it.
One of the latest studies included 255 women with breast cancer and 367 healthy control subjects and compared their answers in a questionnaire on mental outlook and life events. The study results showed that a generally positive outlook seemed to reduce the chances of breast cancer by a quarter.

Additionally, exposure to one or more traumatic life events such as losing a partner or a parent increased the risk by more than 60%.
Researchers believe that women who had been exposed to a number of negative events in their lives belong to "at-risk" group for breast cancer and that negative life events should be considered as risk factor for breast cancer among young women while positive outlooks, feelings of happiness and optimism have a protective role.

On the other hand, Dr Sarah Cant, from Breakthrough Breast Cancer, says that cancer is a complex disease and that there was no clear evidence that positive or negative experiences could affect breast cancer incidence. She defined emotional stress as highly subjective and difficult to measure accurately.

She reported that the women interviewed in the study were already diagnosed with the disease and were therefore more likely to recall feelings of depression and anxiety. Additionally, researchers failed to account other factors known to affect breast cancer risk such as family history and weight.

With breast cancer being a complex disease, it is highly unlikely it had a single cause.