But those who are stressed by their diagnosis may not do as well.

About a third of patients diagnosed with breast cancer suffer anxiety and depression, Three per cent experience post traumatic stress disorder.

US researchers reviewed evidence on how breast cancer patients were affected by stress.

Anxiety, and particularly depression, may actually hamper the patient getting the best treatment

De Lesley Walker, Cancer Research UK

Stress, distress, depression, anxiety and post-traumatic stress disorder have all been linked to reduced immune function and altered hormone balance, while those who have coped well with their diagnosis and treatment have seen improvements in both factors, potentially affecting the outcome of their cancer.

Feeling positive can also help by ensuring that women more follow their cancer treatment regimens more closely, researchers say.

Emotions

Active coping was defined as taking a "direct and rational approach" to a problem, while passive coping involves "indirect approaches such as avoidance, withdrawal and wishful thinking".

Some researcher has suggested active coping has been linked to better immune function and lower levels of the stress hormone cortisol levels, while those who use passive coping strategies have poor immune function and higher cortisol levels.

There is also limited evidence psychotherapy can reduce recurrence and improve survival times.

Dr Linda Luecken, of Arizona State University and Dr Bruce Compas, of Vanderbilt University, write in the journal Annals of Behavioral Medicine: "Interventions focused on improving women's ability to cope with breast cancer diagnosis, treatment and recovery may have beneficial effects on emotional adjustment and potentially on physiological processes.

"There is clear evidence that interventions can have positive effects on emotional adjustment, functional adjustment and treatment of disease-related symptoms."

But Dr Lesley Walker, head of cancer information for Cancer Research UK, told BBC News Online there was conflicting evidence about the effect of stress on cancer patients.

"Women who've been through stressful experiences, such as divorce, actually do as well, if not better, than women who've had a relatively stress-free life."

She added: "Anxiety, and particularly depression, may actually hamper the patient getting the best treatment."