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Oral contraceptives increase breast cancer risk PDF Print E-mail
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Written by Roman Bystrianyk   
Wednesday, 06 December 2006 00:00

Breast cancer is the leading cause of cancer in women worldwide. In the United States breast cancer is the most common cause of cancer death in women aged 20 to 59 years old. Approximately 2 in 15 women in the United States will develop breast cancer during their lifetime and each year nearly 40,000 women die from the disease. Over the last 40 years breast cancer rates have steadily increased worldwide and has increased even faster in developed countries with the rate fastest increase occurring in younger women. 

Oral contraceptive (OC) pills have been commonly used by millions of women in the United States for over 40 years. Oral contraceptives, also commonly known as “The Pill” are a combination of progestin and a synthetic estrogen. This medication that is taken by healthy women to prevent pregnancy and is generally considered by most to be safe and effective. 

However, the World Health Organization (WHO) recently classified both hormone replacement therapy and oral contraceptives as “group 1 carcinogens”. A group 1 carcinogen means that the substance is carcinogenic to humans, whereas group 2A means the substance is probably carcinogenic to humans and group 2B means the substance is possibly carcinogenic to humans.

A study published in the Mayo Clinic Proceedings examined the link between breast cancer and use of oral contraceptives in premenopausal women or women younger than 50 years old. The study authors examined all case-controlled studies conducted from 1980 to the present. 

The authors found that, “the results of the meta-analysis suggest that use of OCs is associated with an increase in breast cancer risk among premenopausal women or women younger than 50 years.” The greatest increase in risk or 50% was for women who used oral contraceptives 4 or more years before their first full term pregnancy. 

The study results agree with previous meta-analyses that were primarily conducted in the 1970s and 1980s. One study published in 1991 in the journal Contraception found an “increased risk of 40%”. Another study published in 1991 found a 60% increased risk of breast cancer for premenopausal women who used oral contraceptives for 96 months or more before their first full term pregnancy. Yet another study published in 1990 in the journal Cancer found that women younger than 46 years old who used oral contraceptives for 4 or more years before their first full term pregnancy had a “72% increased risk”. 

Animal studies have shown that the hormones contained in oral contraceptives are carcinogenic in rodents, dogs, and monkeys. Oral contraceptives have been found to accelerate the rate of breast cell division in women. Increased rates of cell division are associated with increased cancer risk. 

The authors conclude, “consistent with the recent International Agency for Research on Cancer classification of OCs as group 1 carcinogens, this meta-analysis suggests that OCs are associated with an increase risk of premenopausal breast cancer risk, especially among women who use OCs before first full term pregnancy.”


Source: Mayo Clinic Proceedings, October 2006
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Last Updated on Wednesday, 09 September 2009 02:01