Breast cancer is the most common cancer among women in Hong Kong. One in 16 local women are afflicted by breast cancer in their lifetime. While there are various risk factors leading to breast cancer, many of them can be modified by the individuals themselves.
The female hormones which stimulate breast cells to grow are related to breast cancer. The longer the duration that a woman is exposed to these hormones, the higher the risk she develops breast cancer. The Hong Kong Breast Cancer Registry conducted a case-control study on 5,102 patients and 5,520 non-patients whose demographics match those of the patients. By comparing various factors among the two groups, it was found that not giving birth or giving birth to a first child after the age of 35 increases a woman’s risk of developing breast cancer. Comparatively, the risk is lower for a woman who has given birth or had an earlier pregnancy. ‘The level of female hormones is reduced when a woman breastfeeds, thus reducing her risk of breast cancer. The longer duration that a woman breastfeeds, the more the risk is reduced,’ said Prof. Emily Chan of the Jockey Club School of Public Health and Primary Care who led the study.
Hormonal explanation aside, a lack of physical activity and obesity increase the risk of breast cancer. Around 80% of the surveyed patients had less than three hours of exercise per week, while obesity (BMI>25) increased the cancer risk by 46%. More than 40% of the patients reported high levels of stress, i.e., for more than six months in a year, double that of the control group. Diets rich in meat and dairy products also increase the risk.
Like other cancers, family history is a risk factor. ‘For example, BRCA1 mutation may lead to ovarian cancer and breast cancer. Aware that she carried the mutation, actress Angelina Jolie had a double mastectomy to reduce the risk of cancer,’ said Professor Chan. The above research on local cases revealed that only slightly more than 10% of patients had a first-degree relative with breast cancer. Most other risk factors could be modified. It is possible for a woman to reduce the cancer risk by having early pregnancy, breastfeeding, doing exercise, managing stress and maintaining a balanced diet.
This article was originally published in No. 540, Newsletter in Jun 2019.