Suitability of the beagle dog as a test model for the tumorigenic potential of contraceptive steroids. "A short review"

A population-based case-control study of canine mammary tumours and clinical use of medroxyprogesterone acetate

We investigated whether or not an association could be found between mammary tumours and prior clinical use of medroxyprogesterone acetate (MPA) in bitches. A population-based retrospective age-matched case-control study was designed based on interviews with the owners of the bitches. The proportion of bitches with diagnosed mammary tumours (group MT+, n = 98) that had received progestin injections was compared with the proportion in a control group without mammary tumours (group MT-, n = 98). In the case group 39%, and in the control group 21% of the bitches had been treated with MPA. A significantly higher number of bitches with mammary tumours had been exposed to progestins, compared with the control group without mammary tumours (odds ratio = 2.32, Chi-square = 7.01, p = 0.008). Bitches treated clinically with low doses of MPA to avoid oestrus were at a greater risk of developing mammary tumours, the majority of which were histologically malignant (91%).

Pharmacodynamic effects of once-a-month combined injectable contraceptives

The pharmacology and clinical assessment of existing first generation once-a-month combined injectable contraceptives, mainly Deladroxate and Chinese Injectable No. 1, are reviewed. Although these two types of monthly injectables have been used in some million women in China and Latin America, Deladroxate needs indepth re-evaluation of its long-term toxicity and possible accumulation. For injectable No. 1, its disadvantage of being administered on an erratic schedule will cause significant confusion in family planning practice. When used in a strict once-a-month schedule, it is not sufficiently effective for contraception. In order to attain predictable menstrual cycle control as well as high efficacy with a 30-day injection schedule, two improved once-a-month injectable formulations, Cyclofem and Mesigyna, were developed. Pharmacokinetic/pharmacodynamic study on estrogenic components suggested that estradiol valerate and cypionate were suitable estrogen esters to give elevated plasma estrogen levels for 7 to 11 days. After a single injection of Cyclofem and Mesigyna, both formulations showed equal contraceptive effect with inhibition of follicle maturation for some 30 days and ovulation, corpus luteum formation for some 60 days. Multicentre studies on the optimization of dosages of progestogens and estrogens in once-a-month injectables confirmed that the full doses of Cyclofem (DMPA 25 mg/estradiol cypionate 5 mg) and Mesigyna (NET-EN 50 mg/estradiol valerate 5 mg) are suitable for large scale clinical trials. Pharmacodynamics and progestogen/estrogen ratio study indicated the importance of not only the absolute amounts of the progestogen and estrogen but also of their ratio. Reduction of estrogen dose resulted in breakthrough ovulation with both Cyclofem and Mesigyna. Also, it is important to note that the second part of the injection cycle is dominated by the progestogen component of both monthly formulations. A longitudinal study indicated that there is no accumulation of norethisterone after 12 months of treatment with NET-EN 50 mg and estradiol valerate 5 mg.

Combined oral contraceptives containing chlormadinone acetate and breast cancer: results of a case-control study

The main subject of this hospital-based case-control study was the possible relationship between use of combined oral contraceptives (OCs) containing chlormadinone acetate and breast cancer. Analyses were based on data from 490 cases with newly diagnosed breast cancer and 1,223 controls and were separately performed for combined OCs with and without chlormadinone. For either of the combined OCs, risk was not elevated in ever users, did not increase with duration of use and did not change with time since initial exposure or with time since most recent use. However, the relative risk was increased in current users: RR = 1.72 (0.88, 3.36) for combined OCs with chlormadinone and RR = 1.42 (1.01, 2.00) for combined OCs without chlormadinone, which is, however, explained as a screening effect. These results show that chlormadinone as a constituent of combined OCs does not influence breast cancer risk.

Comparative aspects of contraceptive steroids--effects observed in beagle dogs

The effects of oral contraceptives have been studied in the beagle bitch for periods up to 7 yr. High doses of these potent estrogen: progestogen (E:P) combinations have been shown to promote tumors in the mammary glands, smooth muscle of the tubular genitalia, and occasionally in the transitional epithelium of the neck/trigone area of the urinary bladder. The contraceptive formulations used in humans are balanced with an E:P ratio of about 1:5 to 1:80 to produce a desired decidual response in the uterus. The corresponding ratio for producing the decidual reaction in the dog is 1:1,000 to 1:3,000 with the result that the dog is grossly overdosed with estrogens when given the human formulation at the usual multiples of up to 25 times the human dose. Smooth muscle tumors of the tubular reproductive tract are common sequelae to estrogen overstimulation in the dog and are known to occur in other species, including the humans. The dog also has major differences in hormonal control and sensitivity when compared to humans. Progestogens stimulate synthesis and release of growth hormone (GH) in dogs which in turn is the major stimulant (with progestogens) of mammary growth and tumors. Evidence is accumulating which indicates that most if not all progestogens can produce mammary tumors in the dog if given by the correct route and at high enough dosage. In contrast, GH in humans is not increased nor does it have any significant mammotrophic role. Mammary tumors in dogs related to oral contraceptives are now widely considered to be irrelevant as a model or predictor for human tumors. Transitional cell tumors in the urinary bladder seem to be a species specific phenomenon seen on occasion in the dog, but not in the rat, monkey, or human. The usual location in the neck/trigone area may be related to the embryologic origin of this portion of the bladder, which derives from tissues more closely related to the genital organs than does the rest of the bladder.

Oral contraceptives containing chlormadinone acetate and cancer incidence at selected sites in the German Democratic Republic--a correlation analysis

The use of oral contraceptives containing chlormadinone acetate in 1972 by women of 13 districts (out of 15) of the GDR has been related to the incidence of cancer of breast, corpus uteri, and ovary during the period 1961 to 1980. Cancer incidence was represented by cohort parameters showing the risk of the cohorts in relation to each other. No statistically significant association between the two events was noted. Although not significant, our data are consistent with an elevated relative risk for breast cancer of 1.3 and a decreased risk for ovarian cancer of 0.5.

Long acting contraceptives. Present status

Long acting injectable hormonal contraceptives are among the most effective fertility regulating agents developed; yet they are also among the most controversial because of animal data indicating a possible carcinogenic potential in several species. A critical analysis of these animal findings has revealed, in all instances, the existence of specific mechanisms not occurring in the human. For this reason, most national and international scientific bodies who have reviewed this issue have concluded that there are no toxicological reasons for not using long acting hormonal contraceptives. Long acting agents can be divided into 2 separate groups: those having a duration of action of one month, which are composed of a long acting oestrogen and a progestagen, and those lasting for several months which consist of only a progestagen. Among the injectable progestagen-only contraceptives tested, only 2 have so far reached the international market: depot medroxyprogesterone acetate (DMPA), which has been administered at 3- or 6-month intervals and norethisterone enanthate, which has been injected at intervals ranging between 2 and 3 months. The most important side effect observed with these 2 agents is a complete disruption of the menstrual bleeding pattern, leading - in some cases - to total amenorrhoea, which is more frequent with depot medroxyprogesterone acetate than with norethisterone enanthate. The latter, however, has a shorter duration of action with a higher pregnancy rate than the former. Other adverse reactions are rare and of no real importance. Metabolic effects with progestagen-only injectable preparations are, in general, mild and less marked than with combined oestrogen-progestagen formulations. Recent investigations have shown that the return of fertility following their use is delayed but in no way impaired. Monthly injectable oestrogen-progestagen combinations have been tested to a more limited extent and these agents are available only in a very few countries. Their main advantage over progestagen-only preparations is that they allow a reasonable menstrual bleeding pattern in the majority of cases. Their obvious disadvantage is that they contain a long acting oestrogen.

The Depo-Provera debate. Commentary on the article "Depo-Provera, a critical analysis"

A widely publicized article has in recent months caused a great deal of concern among individuals interested in responsible promotion of family planning. The article contains a long series of factual errors, distortions and biased quotations. This commentary presents evidence, based on current knowledge, that Depo-Provera is a satisfactory contraceptive with several advantages and some disadvantages, and poses no more unresolved problems than oral contraceptives. There is no evidence that, at contraceptive doses, it increases the risk of cancer, impairs bone mineralization, "shocks" the hypothalamus, damages the liver or the immune system, or causes premature aging. Studies to date have not shown damaging effects on infants exposed to the drug in utero or via breast milk. To most women, disruption of the menstrual cycle, the major side effect, is not a health hazard. Finally, women in various parts of the world have shown to be quite capable of choosing for themselves whether or not the advantages of the drug can overcome the disadvantage of almost certain menstrual disturbance.