Female breast cancer is so common worldwide that it is very likely you will know someone who has been affected. Although the majority of women who develop breast cancer do so above the age of 50 years, events that take place during puberty can influence this risk.
This blog post was originally an entry by Sabrina Talukdar, from the Institute of Cancer Research, for the Access to Understanding science writing competition hosted by the British Library and Europe PMC. Sabrina's entry to the competition won the People's Choice award and appeared first on the Access to Understanding website. The article that Sabrina's writing is based on is research from the Breakthrough Generations Study - the world's largest, most comprehensive study into the causes of breast cancer.
Why focus on puberty?
Puberty signifies a process of physical changes in response to chemical messengers in the blood, called hormones. In girls, the most important hormone regulating puberty is oestrogen. Oestrogen signals immature breast cells to grow and divide; the appearance of breast buds is usually the first physical sign that puberty has begun. Oestrogen also influences the pubertal growth spurt and the commencement of the first and regular menstrual periods. Puberty can start at different ages and last for different lengths of time.
Oestrogen has a key role in breast cancer; the greater the amount of oestrogen a woman is exposed to over her lifetime, the higher her risks of later developing breast cancer. It has been well established that the earlier the first period (and the later the age of menopause), the higher the risk of developing breast cancer.
Researchers from the Institute of Cancer Research investigated whether the timing of pubertal events, including but not solely focusing on, the age at first menstrual period, had any effect on later breast cancer risk.
How did the researchers carry out their study?
Postal questionnaires were sent to over 100,000 healthy adult women, aged between 16 and 98 years old. The women were asked to recall how old they were when they went through the different stages of puberty (outlined in detail in the questionnaire), as well as about other factors that could influence their risk of breast cancer (for example, lifestyle and family history). The researchers re-contacted the women every two and a half years to find out if any had developed breast cancer. Each woman remained in the study for different lengths of time; on average, for four years. During the study period, over 1,000 women developed breast cancer.
The researchers analysed the group of women as a whole for differences between the average responses of women who had developed breast cancer, compared to those who remained healthy. By recruiting a large group of women to the study, the researchers could be reasonably confident that their responses would be similar to other women in the general population, enabling them to draw strong conclusions.
What did the researchers find?
Women whose breast development started before the age of 10 years, or who reached their final adult height before the age of 14 years had a higher chance of developing breast cancer, compared to women who went through these changes at an older age. A greater than two year gap between the start of breast development and the first period led to a higher chance of developing breast cancer, compared to those with a shorter interval. These increased risks could be the result of a longer period of exposure of immature breast cells to oestrogen, at a very sensitive time for cancerous changes to occur.
If a woman’s periods started or did not become regular until 15 years or over, or if there was a greater than two year gap between the first period and the onset of regular periods, a woman had a lower chance of developing breast cancer, compared to a woman whose periods started earlier or became regular sooner. The researchers suggested that this could be because women in the later-onset group were likely to have lower exposures to oestrogen during this time.
What impact does this research finding have for patients?
The researchers confirmed that early oestrogen-dependent changes during puberty are important determinants of breast cancer risk. There are likely some inaccuracies in the data, as the researchers relied on participants’ memories of events that may have occurred several decades previously. However, this study is arguably more pragmatic than an alternative approach, tracking a group of women from the onset of puberty through until old age. Importantly, the researchers did not have access to information about whether the breast cancers that occurred were responsive to oestrogen. Although the majority of breast cancers are oestrogen-sensitive, a significant proportion do not grow in response to oestrogen; thus exposure during puberty may not be a risk factor for this group of breast cancers.
Children are entering puberty at a much younger age than previous generations; this may explain why the number of cases of breast cancer worldwide is increasing over time. It may be many years before future researchers use the information in the current study to determine if it is safe or indeed desirable to delay pubertal changes to decrease a woman’s later risk of developing breast cancer, however this now presents an intriguing possibility.