Breast Cancer

All women face an increased risk of breast cancer as they age. In fact, breast cancer is more associated with aging than with menopause. It appears most commonly in women age 60 and older; at age 85, women have a one in nine chance of developing the disease. All women are advised to participate in regular breast cancer screening.

Many women considering hormone therapy (HT) to address menopause symptoms are concerned about HT’s potential link to breast cancer. The Society of Obstetricians and Gynaecologists of Canada (SOGC) considers short-term, lowest-dose HT to be safe and effective for the treatment of menopause symptoms, unless a woman has a strong family history of cancer. Public reports about an increased risk of cancer have been misunderstood. In reality, the 24% increased risk of breast cancer reported by the media actually translate into an absolute increased risk of only 8 additional cases per 10,000 hormone users per year in the older age-mix of the WHI study. This level of risk is considered rare by the Council for International Organizations of Medical Sciences, this level of risk is “rare”.

The risk of breast cancer associated with postmenopausal HT is the health risk of greatest concern to women and to their physicians. It is important to put various breast cancer risk factors into perspective. For example, the risks associated with taking HT are about the same as early onset of your period, or a late menopause, as well as a variety of lifestyle-associated risks, such as excessive alcohol consumption and not exercising. Women at midlife are encouraged to pay attention to risk factors you can change by yourself, such as smoking, sedentary lifestyle, excessive intake of alcohol, and postmenopausal weight gain. Addressing these things will help you reduce adverse risks at this time in your life.

When evaluating whether HT is right for you, consult your health-care provider.

Assess your risk: National Cancer Institute breast cancer risk assessment tool.


Cumulative absolute risk and additional risk of breast cancer with duration of use of hormone therapy
Three to five percent of women with a predisposition to breast cancer carry a specific genetic mutation (BRCA1 or 2) that increases their lifetime risk of developing the disease to between 60 and 80 percent. Recent findings suggest that HT is not associated with an increased risk of cancer in these women; in postmenopausal women it is associated with a decreased risk.
Age at calculation (years)
Age range (years) Risk with no hormone replacement therapy Additional risk (%) with combination therapy* (%) with oestrogen only therapy* (years of use)
Ratio % 3 years 5 years 10 years 15 years 3 years 5 years 10 years 15 years
40 40-79 1 in 14 7.21 0.18 0.38 1.18 2.22 0.05 0.12 0.34 0.64
45 45-79 1 in 15 6.76 0.26 0.52 1.45 2.54 0.07 0.15 0.41 0.73
50 50-79 1 in 16 6.10 0.31 0.60 1.59 2.82 0.09 0.18 0.45 0.81
55 55-79 1 in 19 5.30 0.33 0.64 1.76 3.17 0.09 0.19 0.50 0.91
60 60-79 1 in 23 4.44 0.37 0.73 2.01 3.51 0.10 0.21 0.57 1.00
65 65-79 1 in 29 3.48 0.42 0.84 2.19 3.27 0.12 0.25 0.62 0.91
70 70-79 1 in 42 2.37 0.47 0.88 1.64 - 0.13 0.25 0.50 -
75 75-79 1 in 88 1.14 0.43 0.58 - - 0.12 0.14 - -


*The additional risk for a specific formulation and duration of use can be added to the baseline risk with no hormone therapy to provide an estimate of a woman’s specific cumulative absolute risk of breast cancer from a specific age to age 79 years.

†The ratio is calculated as the reciprocal of the cumulative absolute breast cancer risk (%) of non-users.

"The greatest single risk factor for breast cancer, after gender and advancing age, is the presence of two or more affected first order relatives. There are a number of commonly experienced risk factors including being 20 per cent overweight, delaying childbirth until 30 or older, consuming two glasses of alcohol daily, and lack of regular exercise. Long-term use of HT is of comparable magnitude to this group of risk factors."

SOGC 2006 Menopause Consensus Report

Read this article on What you should eat (and avoid) to beat breast cancer.

Ontario Breast Screening Program - 2011 Report

Endometrial cancer

While there has been discussion about the link between estrogen and the risk of endometrial cancer, recent evidence suggests that low-dose estrogen therapy for the treatment of menopause symptoms has a minimal effect on the risk of endometrial cancer. Research also shows HT does not increase the risk of recurrence among women with a history of early stage, low-grade endometrial cancer. Although estrogen and progestin can influence the growth of fibroids (benign tumours that typically form on the wall of the uterus), HT doses are usually low enough that they have no effect.

Combined estrogen/progestin therapy offers some reduction in endometrial cancer risk for women who have not undergone a hysterectomy.

Colorectal cancer

The long-term use of hormone replacement therapy may substantially cut the risk of colorectal cancer, research shows.

The greatest risk reduction - 48 percent - was observed among women who had used a combined estrogen plus progestin hormone regimen for two to five years, according to a report in Cancer Epidemiology, Biomarkers and Prevention, published by the American Association for Cancer Research. Despite the decrease in use of HT due to confusion regarding its relation to breast cancer, this research suggests an important protective effect of all hormone formulations. The current findings stem from a study looking at data for 56,733 women followed for an average of 15 years, among whom 960 were diagnosed with colorectal cancer. The average age at the first interview conducted from 1979 to 1981 was 55.7 years. Any use of estrogen therapy was associated with a 17 percent reduced risk in colorectal cancer, the investigators found. Among women who used estrogen, the largest reductions were seen among those who were current users (25 percent reduced risk) and users of 10 or more years duration (26 percent reduced risk).

Find out more

Back to top



Among postmenopausal women with a BRCA1 mutation, HT use was not associated with increased risk of breast cancer; indeed, in this population, it was associated with a decreased risk.

J Natl Cancer Inst. 2008