Induced abortion as cancer risk factor: a review of epidemiological evidence.

In spite of the fact that efficient contraception is available in many countries, induced abortion is still a quite prevalent means of birth control, especially in certain subpopulations of women (young, socially deprived, etc). Judging by the published statistics, induced abortion rates vary dramatically between countries, with the lowest level being in West Germany (5-7 per 1000 women aged 15-441) and the highest in the Russian Federation of the USSR (123-6 in the mid-80s2). Ever since its legalisation in 1955, induced abortion has been the primary means to reduce fertility in the USSR, resulting in 7 116 000 terminations in this country in 1986 (compared with only about 5 611 000 livebirths2), or 101 2 per 1000 women of reproductive age.2 The real prevalence of induced abortion in the USSR is even higher than reflected by official statistics, since there is substantial underreporting in many areas, especially for the youngest and primigravid women.3 Results of a few surveys suggest that on average a sexually active woman has 2-4 induced abortions by the end of her reproductive period, and roughly 10-15% ofthe women have their first pregnancy interrupted.3 Induced abortion rates are highly differentiated between national, regional, and social subgroups of the population. Thus the range of variation between the national republics in registered induced abortion rates in 1985 was fourfold, ie, 30-8% in Azerbaidjan versus 123-6% in the Russian Federation.2 Sociodemographic and public health implications of multiple induced abortion in the USSR are well known: fertility reduction due to secondary postabortive sterility/subfecundity, high prevalence of chronic gynaecological conditions in young and middle aged women, obstetric complications, and high infant mortality.5 But up to now, clinical (and a few epidemiological) investigations have been focused on immediate and short term complications of induced abortion and its influence on subsequent reproductive function,5 while the long term cumulative effect of pregnancy termination has hardly been assessed. The issue of possible oncological implications of induced abortion discussed in this paper has traditionally been "no man's land" in a highly specialised medical science, as it has been missing from the curriculum of both oncologists and gynaecologists. Epidemiologically, induced abortion has also been neglected as a specific risk factor involved in causation of sex hormone related cancers in women. To my knowledge, no study in this area has examined the potential effect of induced abortion in relation to length of gestation, termination procedure used, presence of immediate complications, etc. This lack of attention is not easy to understand, since involvement of induced abortion in some stage of carcinogenesis in hormone dependent organs is biologically highly plausible. Some clinical and laboratory studies have shown that sudden interruption of the endocrine, immunological, neurological and other processes which adjust the organism to coexistence with the fetus cause a strong and long lasting impact, described by some investigators as a "hormonal blow".4 In cases of repeated induced abortion, such changes may accumulate, gradually producing chronic hormonal changes (such as progesterone deficiency) and/or immune disorders, to which psychological depression caused by this dramatic life event may also contribute.45 These shifts may lead to disturbance of mechanisms of cell differentiation and proliferation, weakening of immunity, and other systemic changes involved in malignant transformation.468 Therefore considering induced abortion in epidemiological analysis as just another short term pregnancy rather than a specific biological event may be misleading.