Breast Cancer Risks, Oral Contraception

Second Chapter

The risk of breast cancer

The risk of breast cancer in oral contraceptive users is one of the most controversial topics (102,164,165,166,167).

Most cases of breast cancer occur in the unit formed by the lobes and excretory ducts of the mammary gland (81). It was estimated that in 1980 there were 572,000 new cases of breast cancer in the world. The incidence curve increases from 30 to 70 years of age with a slight inflection between 45 and 54 years of age (81).

Risk factors for breast cancer are: high socioeconomic level, nulliparity, late first birth, early menarche, late menopause, history of benign breast disease and family history of breast cancer.

The main causes of breast cancer remain unknown, however endogenous hormones seem to play an important role in the pathogenesis (81). The hormonal dependence of breast cancer is today beyond doubt and is a fundamental focus in research into its etiology.

Breast cancer appears to be multifactorial. Today it is accepted that both components of combined oral contraceptives constitute a hormonal risk factor for breast cancer and not just estrogen as previously thought (83,102,164).

In 17 of 18 case-control studies and in 5 cohort studies, analyzed by experts from the World Health Organization (81), no important changes in the risk of breast cancer were observed when comparing women who had used oral contraceptives at any time. once with women who had never received them. Studying users by age sub-groups, inconsistent reports have been obtained.

When breast cancer is diagnosed in young women:

Before the age of 35, a slight increase has been found in the relationship with the history of use of combined oral contraceptives, especially for prolonged periods (13,165), as was evidenced in the National Case-Control Study carried out in the United Kingdom. United and published in 1989, where they estimated that the relative risk is 1.4 with 4 to 8 years of use and 1.7 with more than 8 years of use.

Studies relating the risk of breast cancer to the use of combined oral contraceptives started before age 25, or before the first full-term pregnancy, are contradictory (81).

However, Balasch and Calaf (83) suggest that in order to try to reduce the risk of breast cancer associated with the use of oral contraceptives, prolonged use should be discouraged in adolescents, who usually postpone their first pregnancy until after the age of 30.

(Read Also: Risks of Cervical Neoplasia)

Many case-control studies have shown that in mid- and late reproductive life:

The use of this method does not influence the risk of breast cancer. In women over 35 years of age or in those who have not carried a pregnancy to term, the results are contradictory. While some show no impact, others point to an increase in the incidence of breast carcinoma (166,167). There are indications that the risk associated with the consumption of microdose oral contraceptives is lower than that attributed to contraceptives containing 50 or more ug/day of ethinyl estradiol.

In 1996, the Collaborative Group on Hormonal Factor in Breast Cancer (166) gathered data from 54 studies, almost 90% of the epidemiological studies carried out worldwide, grouping 53,297 women with breast cancer and 100,239 controls without breast cancer and concluded that current oral contraceptive users are at a slightly higher risk of breast cancer, relative risk of 1.24 (CI: 1.15 – 1.33). When the use of the pill is discontinued, the RR progressively decreases to 1.16 after 1-4 years, to 1.07 after 4-9 years and disappears after 10 years.

This pattern is independent of the duration of use. The same behavior was observed among women with risk factors such as nulliparity or family history of breast cancer, among women from developed or developing countries, and in different ethnicities (168). In this same study (166) they determined that women who started using oral contraceptives before the age of 20 had higher risks than those who started later.

The relative risk of breast cancer for current use is 1.59. The RR decreases to 1.4 1-4 years after discontinuing use and at 5 years the difference between women who started use early or later has disappeared (168). At the same time, ten or more years after stopping oral contraceptives, there are no differences in the cumulative risk of breast cancer between women who have ever used combined oral contraceptives and those who have never used them (164).

On its website, the National Cancer Institute believes that the slightly elevated risk while using the pill may be a result of estrogen’s ability to promote the growth of cancer cells already present in the breast, rather than a potential ability to initiate new evil points.

However, the National Cancer Institute says that cancer risk more typically peaks decades after exposure, rather than immediately afterward.

Cancer is generally more likely to occur due to a prolonged duration and/or high degree of exposure to a carcinogen. In the aforementioned study (166) neither the hormonal concentration nor the duration of use affected the result. In many circumstances the dangers of unwanted pregnancy far outweigh the small increase in breast cancer risk associated with oral contraceptive use (168).

Dueñas Díez (86) considers that the increase in the risk of breast cancer derived from the use of oral contraceptives, observed in some meta-analyses, is negligible for two reasons: the first, because when this supposed increase is translated into the number of women , this is insignificant, and secondly, because the margin of error of the meta-analysis technique itself can be up to 25%. Dueñas Díez (86) also asserts that it does not seem justified to affirm that the use of oral contraceptives increases the risk of breast cancer.

Marchbanks et al published in 2002 (169) the results of Women’s Contraceptive and Reproductive Experiences (Women’s CARE), a study carried out in women between 35 and 64 years of age to establish the risk of breast cancer with oral contraceptives and It is observed that the relative risk obtained was 1.0 (CI: 0.8 – 1.3) for current users and 0.9 (CI: 0.8 – 1.0) for past users, results that are similar to those obtained in the study published in 1986 by “The Cancer and Steroid Hormone” (CASH), where it was shown that there was no association between the use of combined oral contraceptives and breast cancer (1).

In his textbook, Speroff (7) points out three aspects that are worth reproducing:

Breast Cancer Risks, Oral Contraception

By Guhiy

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