PILLS and CANCER

Birth control pills (so called "pills") first became available to American women in the early 1960s. The convenience, effectiveness, and reversibility of action of birth control pills have made them the most popular form of birth control in the United States. However, concerns have been raised about the role that the hormones in pills might play in a number of cancers, and how hormone-based pills contribute to their development. Sufficient time has elapsed since the introduction of pills to allow investigators to study large numbers of women who took birth control pills for many years.

Some studies have shown an increased risk of breast cancer in women taking birth control pills, while other studies have shown no change in risk Birth control pills use has been shown in multiple studies to decrease the risk of ovarian and endometrial cancer Birth control pills have been shown to increase the risk of cervical cancer; however, human papillomavirus is the major risk factor for this disease The risk of liver cancer is increased in women who take birth control pills and are otherwise considered low risk for the disease

Estrogen stimulates the growth and development of the uterus at puberty, causes the endometrium (the inner lining of the uterus) to thicken during the first half of the menstrual cycle, and influences breast tissue throughout life, but particularly from puberty to menopause.

Progesterone, which is produced during the last half of the menstrual cycle, prepares the endometrium to receive the egg. If the egg is fertilized, progesterone secretion continues, preventing release of additional eggs from the ovaries. For this reason, progesterone is called the “pregnancy-supporting” hormone, and scientists believe that it has valuable contraceptive effects. The man-made progesterone used in pills is called progestogen or progestin.

Because medical research suggests that some cancers depend on naturally occurring sex hormones for their development and growth, scientists have been investigating a possible link between pills use and cancer risk. Researchers have focused a great deal of attention on pills users over the past 40 years. This scrutiny has produced a wealth of data on pills use and the development of certain cancers, although results of these studies have not always been consistent. The risk of endometrial and ovarian cancers is reduced with the use of pills, while the risk of breast and cervical cancers is increased.

How do Birth control pills affect breast cancer risk?

A woman’s risk of developing breast cancer depends on several factors, some of which are related to her natural hormones. Hormonal factors that increase the risk of breast cancer include conditions that may allow high levels of hormones to persist for long periods of time, such as beginning menstruation at an early age (before age 12), experiencing menopause at a late age (after age 55), having a first child after age 30, and not having children at all.

A 1996 analysis of worldwide epidemiologic data conducted by the Collaborative Group on Hormonal Factors in Breast Cancer found that women who were current or recent users of birth control pills had a slightly elevated risk of developing breast cancer. The risk was highest for women who started using OCs as teenagers. However, 10 or more years after women stopped using pills, their risk of developing breast cancer returned to the same level as if they had never used birth control pills, regardless of family history of breast cancer, reproductive history, geographic area of residence, ethnic background, differences in study design, dose and type of hormone, or duration of use. In addition, breast cancers diagnosed in women after 10 or more years of not using pills were less advanced than breast cancers diagnosed in women who had never used pills.

The findings of the Women’s Contraceptive and Reproductive Experiences (Women’s CARE) study were in contrast to those described above. The Women’s CARE study examined the use of pills as a risk factor for breast cancer in women ages 35 to 64. Investigators collected detailed information about the participants’ use of pills, reproductive history, health, and family history. The results, which were published in 2002, indicated that current or former use of pills did not significantly increase the risk of breast cancer. The findings were similar for white and black women. Factors such as longer periods of use, higher doses of estrogen, initiation of pills use before age 20, and pills use by women with a family history of breast cancer were not associated with an increased risk of the disease.

In a National Cancer Institute (NCI)-sponsored study published in 2003, researchers examined risk factors for breast cancer among women ages 20 to 34 compared with women ages 35 to 54. Women diagnosed with breast cancer were asked whether they had used pills for more than 6 months before diagnosis and, if so, whether the most recent use had been within 5 years, 5 to 10 years, or more than 10 years. The results indicated that the risk was highest for women who used pills within 5 years prior to diagnosis, particularly in the younger group.

How do Birth control pills affect ovarian and endometrial cancer risk?

Studies have consistently shown that using pills reduces the risk of ovarian cancer. In a 1992 analysis of 20 studies of pills use and ovarian cancer, researchers from Harvard Medical School found that the risk of ovarian cancer decreased with increasing duration of pills use. Results showed a 10 to 12 percent decrease in risk after 1 year of use, and approximately a 50 percent decrease after 5 years of use.

Researchers have studied how the amount or type of hormones in pills affects ovarian cancer risk reduction. One of the studies used in the Harvard analysis, the Cancer and Steroid Hormone Study (CASH), found that the reduction in ovarian cancer risk was the same regardless of the type or amount of estrogen or progestin in the pill. A more recent analysis of data from the CASH study, however, indicated that pills formulations with high levels of progestin reduced ovarian cancer risk more than preparations with low progestin levels. In another recent study, the Steroid Hormones and Reproductions (SHARE) study, researchers investigated new, lower-dose progestins that have varying androgenic properties (testosterone-like effects). They found no difference in ovarian cancer risk between androgenic and nonandrogenic pills.

The use of pills has been shown to significantly reduce the risk of endometrial cancer. This protective effect increases with the length of time pills are used, and continues for many years after a woman stops using pills.

How do Birth control pills affect cervical cancer risk?

Evidence shows that long-term use of pills (5 or more years) may be associated with an increased risk of cancer of the cervix (the narrow, lower portion of the uterus). Although pills use may increase the risk of cervical cancer, human papillomavirus (HPV) is recognized as the major cause of this disease. Approximately 14 types of HPV have been identified as having the potential to cause cancer, and HPVs have been found in 99 percent of cervical cancer biopsy specimens worldwide.

A 2003 analysis by the International Agency for Research on Cancer (IARC) found an increased risk of cervical cancer with longer use of pills. The data suggested that the risk of cervical cancer may decrease after pills use stops. In another IARC report, data from eight studies were combined to assess the effect of pills use on cervical cancer risk in HPV-positive women. Researchers found a fourfold increase in risk among women who had used pills for longer than 5 years. Risk was also increased among women who began using pills before age 20 and women who had used pills within the past 5 years.

How do Birth control pills affect liver cancer risk?

Several studies have found that pills increase the risk of liver cancer in populations usually considered low risk, such as white women in the United States and Europe who do not have liver disease. In these studies, women who used pills for longer periods of time were found to be at increased risk for liver cancer. However, pills did not increase the risk of liver cancer in Asian and African women, who are considered high risk for this disease. Researchers believe this is because other risk factors, such as hepatitis infection, outweigh the effect of pills.

What screening tests are available for the cancers described?

Studies have found that regular breast cancer screening with mammograms reduces the number of deaths from breast cancer for women ages 40 to 69.  Women who are at increased risk for breast cancer should seek medical advice about when to begin having mammograms and how often to be screened. A high-quality mammogram, with a clinical breast exam (an exam done by a professional health care provider), is the most effective way to detect breast cancer early.

Abnormal changes in the cervix can often be detected by a Pap test and treated before cancer develops. Women who have begun to have sexual intercourse or are age 21 should check with their doctor about having a Pap test.

Women who are concerned about their risk for cancer are encouraged to talk with their health care provider.

(Info from National Cancer Institute - http://www.cancer.gov/cancertopics/factsheet/Risk/oral-contraceptives)