June 29th, 2012 by Hasham

Epidemiology And risk Factors For Breast Cancer

INTRODUCTION

In the US, breast cancer is the most common female cancer, the second most common cause of cancer death in women, and the main cause of death in women ages 40 to 59. About one-half of cases can be explained by known risk factors, such as age at menarche, first live birth, menopause, and proliferative breast disease. An additional 10 percent are associated with a positive family history.

Understanding the risk factors for breast cancer permits us to identify women at increased risk and to intervene to modify risk, both individually and societally.

EPIDEMIOLOGY

Incidence — Approximately 230,000 new cases of invasive breast cancer are expected to be diagnosed in the United States in 2012, and almost 40,000 will die from the disease [1]. The lifetime probability of developing breast cancer is one in six overall (one in eight for invasive disease) [2].

In the early 1980s, breast cancer rates rose steeply by 3.7 percent per year over the baseline incidence. This was most likely the result of increasing use of screening mammography, since the incidence of ductal carcinoma in situ (DCIS) and stage I carcinomas increased, while that of higher stages either decreased or remained stable. After increasing from 1994 to 1999, breast cancer incidence rates decreased from 1999 to 2007 by 1.8 percent per year .

Potential contributory factors to this decline include discontinuation of hormone therapy (HT) due to the data from the Women’s Health Initiative (WHI) linking HT and breast cancer, and saturation/leveling off of mammography rates [4-7]. Discontinuation of HT has probably had a greater effect [6,8,9]. The WHI reported their data on breast cancer risk in the post-intervention phase of the randomized trial (HT versus placebo) and in the observational (HT users versus nonusers) cohort . In both groups, there was a rapid decline in breast cancer incidence after discontinuation of HT. Changes in mammography utilization were unlikely to have contributed to the decrease, since post-intervention mammography rates were similar in both the HT and control arms of the randomized trial, and mammography rates did not fluctuate over time in the observational cohort.

Breast cancer – risk factors

This page contains information on breast cancer risk. A substantial proportion of the breast cancer cases experienced in developed countries can be explained by factors which influence exposure to oestrogen, including reproductive and hormonal factors, obesity, alcohol and physical activity. A study published in December 2011 estimated that, in the UK, around 27% of female breast cancers are linked to largely modifiable lifestyle and environmental factors. Some reproductive factors, such as age at first child and number of children, were not included in this analysis.

Endogenous hormones

Higher levels of endogenous hormones have long been hypothesized to increase breast cancer risk. Studies show that post-menopausal women with the highest levels of oestrogen and testosterone have 2-3 times the risk of women with the lowest levels.17 The link between these hormones and pre-menopausal breast cancer risk is less clear.18,19 Higher levels of the hormone, prolactin, have been associated with an increased risk of breast cancer, particularly oestrogen-receptor-positive tumours.20 Having higher levels of insulin has been associated with an increased risk of post-menopausal breast cancer in women not taking hormone replacement therapy.21  A link between high insulin levels and breast cancer might explain the 20% increased risk of breast cancer for women with diabetes shown in a meta-analysis.87 Insulin-like growth factor 1 is positively associated with breast cancer risk

Previous breast disease

Benign breast disease is a generic term describing all non-malignant breast conditions, some of which carry an increased risk for breast cancer while others do not. Women with proliferative breast disease without atypia have a two-fold increased risk, whilst those with atypical hyperplasia have a more that four-fold increased risk. 33

Women with a strong family history and nonproliferative breast lesions have a 60% increase in risk of breast cancer, but there is no risk increase for women without a family history.33 (In this study the criteria for a strong family history includes women with at least one first-degree relative with breast cancer before the age of 50 years or two or more relatives with breast cancer, with at least one being a first-degree relative). Women are more likely to develop breast cancer in the same breast as the benign breast lesion than in the opposite breast. 33,34

Ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS) are non-invasive conditions of the breast, which can in some cases develop into invasive cancer. Although women with in situdisease are more likely to develop invasive disease, it is difficult to know which are going to, although it is more likely to occur with high grade than low grade DCIS lesions.35  Overall, women with a previous in situ tumour have double the risk of invasive breast cancer compared to the general population, higher in the same breast as the carcinoma in situ than in the other breast.86

A previous diagnosis of breast cancer raises the risk of developing a second primary breast cancer. Risk ratios vary from a 40% risk increase36,37 to almost five-fold risk increase.38,79 A recent analysis suggests that a substantial proportion of contralateral breast cancers (CBC) diagnosed within two years of the first breast cancer may be in actual fact tumour spread from the primary breast cancer, and two years may be an appropriate cut-off for separating independent breast cancers from those that have spread from a previous breast cancer.79 Nonetheless, risk of CBC remains higher two or more years after a primary breast cancer, particularly where the first breast cancer was diagnosed before the age of 40.79 Risk of CBC is higher for women whose first tumour was hormone-receptor negative compared to those with a previous hormone-receptor-positive tumour, according to a recent study. 80 A recent randomised trial has shown that taking tamoxifen for five years, rather than two, can reduce risk of CBC by 30%.

Abstract

Breast cancer is the most common form of cancer and the principal cause of death from cancer among women worldwide. Risk factors for breast cancer are manifold. Certain risk factors, such as age and family history are well established. Research in the past decade has further elucidated disease aetiology, in particular the role of hormones and the discovery of breast cancer susceptibility genes (e.g. BRCA1, BRCA2). In spite of the evidence concerning the risks of breast cancer, women often have a poor understanding of its causes and limited personal risk perception. The media are an important source of health information for many women, but the popular and general-interest media often misrepresent risk factors. Knowledge of breast cancer risk factors and perception of personal risk are significant behaviour motivators to prevent, detect and manage disease. This article will review the risk factors for breast cancer, and examine the research on women’s perception of risk and understanding of risk factors, and the reporting of breast cancer in the media.