Treatment of feline mammary fibroadenomatous hyperplasia with a progesterone-antagonist

Recurrent Feline Mammary Fibroadenomatous Hyperplasia in a Cat During Gestation

Feline mammary fibroadenomatous hyperplasia (FMFH) is an extensive proliferation of feline mammary tissues in response to endogenous or exogenous progestogens. The treatment of choice for FMFH is anti-progestins or ovariohysterectomy (OVH). OVH if there is no intention of breeding the queen. This report describes a case of recurrent FMFH in an 11-month-old female Maine Coon cat. The condition was successfully treated with aglepristone during its first occurrence but recurred during the cat's subsequent gestation. OVH was performed along with aglepristone administration, resulting in complete regression of FMFH 21 days after aglepristone injection. The recurrence of FMFH successful treatment is well described; however, this case illustrates the necessity for further discussion regarding the utilisation of cats previously diagnosed with FMFH for breeding purposes.

Reversible control of reproduction in tom cats: medical options for manipulating libido and fertility

BACKGROUND

There has been a growing interest in alternatives to surgery for controlling reproduction in tom cats, and the resultant medical options add to a practitioner's toolbox when handling these cases in clinical practice. It is important, however, that when suggesting these drugs, veterinarians have a good understanding of their mode of action, and their correct use and dosage.

CLINICAL RELEVANCE

Breeders increasingly wish to be able to switch on/off the reproductive ability of their tom cats in a controlled manner. In addition, in small animal medicine, there has been concern from some academics, and a growing number of pet cat owners, about potential long-term effects of surgical sterilisation. Further, for some cats surgical castration may not be possible due to health conditions that mean anaesthesia is unsafe. In all of these scenarios, medical alternatives to surgery can prove useful.

EQUIPMENT AND TECHNICAL SKILLS

No special equipment or technical skills are required. A good knowledge of the medical alternatives to surgical sterilisation for controlling reproduction in a tom, and making sure the patient is a suitable candidate, are, however, important for ensuring the cat's health during and after treatment and the owner's satisfaction.

AUDIENCE

This review is aimed principally (but not exclusively) at veterinary practitioners working with cat breeders who seek a temporary arrest in their tom cat's reproduction. It may also help practitioners with clients who would like an alternative to surgery or with cats where anaesthesia for surgical castration is not possible.

EVIDENCE BASE

Advances in reproductive feline medicine have resulted in improved knowledge of medical contraception. This review draws on scientific evidence-based papers that report on the mode of action, length of efficacy and potential side effects of different methods of medical contraception, as well as the authors' own clinical experience.

Gynaecomastia in a male neutered cat with an adrenal tumour and associated hyperprogesteronism, hypercortisolism and hyperaldosteronism

Case summary

A 7-year-old male neutered domestic longhair cat was presented with chronic progressive gynaecomastia, polydipsia, polyphagia, weight loss and poor fur regrowth. Sexualised behavioural changes were not reported and virilisation was not present on physical examination. Pertinent haematology, biochemistry and urinalysis findings at the time of referral included mild hypokalaemia. Left adrenomegaly and mild prostatomegaly were identified on a CT scan. Evaluation of adrenal hormones with a low-dose dexamethasone suppression test, serum progesterone, testosterone, oestradiol, plasma aldosterone, renin, plasma metanephrine and normetanephrine measurement supported a diagnosis of hyperprogesteronism, hyperaldosteronism and hypercortisolism. Adrenalectomy was performed and histopathology was consistent with an adrenocortical tumour. Clinical signs and hormone elevations resolved postoperatively.

Relevance and novel information

To our knowledge, this is the second report of gynaecomastia secondary to an adrenal tumour in a male neutered cat and the first associated with hyperprogesteronism.

Conservative treatments for feline fibroadenomatous changes of the mammary gland

Background:

Fibroadenomatous changes (FAC) of the mammary gland in cats represents a benign, progesterone-associated fibroglandular proliferation of one or more mammary glands that may occur in intact female cats at the time of puberty, during pregnancy or pseudopregnancy, or in female and male cats of any age under progestin treatment. Nowadays, the elective treatment of FAC is based on the progesterone antagonist aglepristone. This study aimed to report the treatment of FAC with a combination of drugs designed to preserve mammary gland integrity, even in pregnant cats.

Case Description:

Eight sexually intact female cats with FAC showed mammary glands that were symmetrically enlarged and inflamed in all cases, and the skin was ulcerated in six cats. Four cats were on days 25–32 of pregnancy at presentation. Non-pregnant cats were treated with aglepristone and with a dietary supplement containing maltodextrin and bromelain. The mammary glands were massaged daily with an Aloe vera emollient gel. If the gland was inflamed or ulcerated, broad-spectrum antimicrobial, and anti-inflammatory treatments were given, and the ulcers were treated topically with a hypericum and neem-based cream. Two of the four pregnant cats were treated with the same therapeutic schedule plus cloprostenol to facilitate uterine emptying. Two pregnant cats underwent the same protocol except for aglepristone, which was not administered to safeguard the litter and see if the adjuvant therapy worked independently. At term, they delivered four and three kittens, respectively, that were normally nursed and weaned after 40 days. In all the studied cases, the mammary gland reduced in size 2–3 weeks after the start of the treatment and completely remitted after 4–5 weeks.

Conclusion:

This case series encourages adjuvant therapy in the course of FAC to preserve mammary gland integrity and functionality. Exploiting the natural decline of progesterone at the end of pregnancy (or pseudopregnancy), the therapy may also be used without aglepristone, when its use has other limitations.

Effectiveness of ovariohysterectomy on feline mammary fibroepithelial hyperplasia treatment

OBJECTIVES

The aim of this study was to evaluate the effectiveness of ovariohysterectomy (OVH) on feline mammary fibroepithelial hyperplasia (FMFH) treatment, as well as the influence of previous injectable progestin on clinical signs and treatment of FMFH.

METHODS

Seventy-nine female cats diagnosed with FMFH between 2014 and 2018 were included. The animals were distributed as follows: (1) treated only with OVH (TA) or OVH plus antiprogestin (TB); and (2) no administration (G1) or previous administration (G2) of injectable progestin before FMFH diagnosis. Data regarding clinical signs of FMFH, occurrence of persistent mammary growth after OVH, and time until complete remission of FMFH post-surgery were recorded and evaluated.

RESULTS

Mastectomy was not performed in any cat during the study. TA was adopted in 71/79 (89.9%) cases, with 42/71 (59.2%) from G2 and 29/71 (40.8%) from G1. TB was adopted in 8/79 (10.1%) cats, all from G2. Total remission of FMFH was observed in 73/79 (92.4%) cats, with six animals from G2 having died (n = 6/79 [7.6%]). The time until complete remission of FMFH was higher (P <0.0001) in cats from G2 than from G1. Moreover, animals from G2 had a higher percentage of persistent mammary growth after OVH (P <0.001) and a tendency to higher mortality (P = 0.052) compared with G1.

CONCLUSIONS AND RELEVANCE

Previous treatment with injectable progestin may result in a more complex clinical presentation of FMFH. Ovariohysterectomy is a good treatment option for FMFH when there is no interest in breeding the queen. Treatment with antiprogestin is recommended, especially if persistent mammary growth is detected after OVH.

Decreased Size of Mammary Tumors Caused by Preoperative Treatment with Aglepristone in Female Domestic Dogs (Canis familiaris) Do Not Influence the Density of the Benign Neoplastic Tissue Measured Using Shear Wave Elastography Technique

Shear wave elastography (SWE) can be useful to discriminate between malignant and benign mammary tumors. In dogs with elevated progesterone levels compared to the baseline and fast-growing tumors, treatment with the use of aglepristone allows for tumor size reduction, which facilitates surgery. This study aimed to evaluate the influence of the preoperative treatment of benign mammary tumors (BMTs), performed with the use of aglepristone, on the density of the tumor tissue measured by SWE. Twelve female dogs with diagnosed BMTs and increased levels of progesterone were treated with aglepristone (Alizine, Virbac, France) at 10 mg/kg s.c. (Subcutaneous injection). twice, with a 24 h interval. The density of the tumor was evaluated by SWE before and after the treatment. The type of tumor was evaluated by fine needle aspiration cytology before treatment, and a histopathological examination was made after surgical removal, performed after the aglepristone treatment. In all the cases, a significant reduction in the mammary tumor's size was observed following treatment, with no influence on the density of the tumor's tissue measured by SWE. Similar studies on malignant mammary tumors are warranted to verify if in these cases, density will also be a constant parameter that is not dependent on the tumor size.

Contraceptive implants used by cat breeders in France: a study of 140 purebred cats

OBJECTIVES

Deslorelin 4.7 mg and melatonin 18 mg subcutaneous implants were studied in purebred male and female cats, via questionnaires sent to French cat breeders, to assess breed, age, duration of the contraceptive effect, fertility after use, changes in behaviour and side effects.

METHODS

Reproductive data were collected in 57 tom cats and 41 queens implanted with deslorelin 4.7 mg, and 42 queens implanted with melatonin 18 mg, for a total of 140 purebred cats, from 38 different catteries, representing 18 breeds.

RESULTS

Using deslorelin (Suprelorin 4.7 mg; Virbac), sexual behaviour in males was inhibited for a mean ± SD of 13.4 ± 3.2 (range 8-21) months in 37/57 cats. Of these, 24/37 mated successfully and produced litters at a mean of 15.5 ± 3.6 (range 9-20) months. Inhibition lasted 11 ± 1.1 (range 9-12; n = 6), 13.2 ± 2.4 (range 12-18; n = 6) and 15 ± 3.5 (range 9-18; n = 6) months in Norwegian Forest Cat, Singapura and Ragdoll males, respectively. In 26/41 females implanted with deslorelin 4.7 mg, oestrus was inhibited for a mean of 16.0 ± 5.7 (8-38) months; 12/26 went on to produce a litter. Of the side effects specific to females: two presented persistent oestrus, leading to the removal of the implant; two developed lactation; one had fibroadenomatosis; and one was sterilised owing to cystic endometrial hyperplasia. Using melatonin (Melovine 18 mg; Ceva), 33/42 females had oestrus inhibited for a mean of 86 ± 50 (range 21-277) days after implantation with a peak return to oestrus in March, and 12/33 had a subsequent litter. No side effects were reported.

CONCLUSIONS AND RELEVANCE

This study is the first to collect a large amount of field data, in 140 purebred male and female cats where a deslorelin 4.7 mg or a melatonin 18 mg implant was used. These field results may allow for more accurate clinical advice and open up new avenues of research.

Mammary fibroadenomatous hyperplasia in a male cat

Case summary

Mammary fibroadenomatous hyperplasia (MFH) is a benign pathology characterised by extensive proliferation of the ductal epithelium and mammary stroma. It typically occurs in young female cats, and seems to result from hypersensitivity to progesterone. A 2-year-old entire male European Shorthair cat presented to the veterinary clinic with enlargement of several mammary glands, which had developed within the previous 10 days. There was no prior administration of progestin in the cat’s medical history. Diagnostic tests were performed to assess the basal progesterone concentration and the concentration after stimulation with gonadotropin-releasing hormone, which ruled out the presence of functional ovarian tissue. Histological examination of the testes excluded hormone-secreting testicular tumours. Histological examination of the mammary gland confirmed the diagnosis of MFH. Treatment was started with aglepristone, a selective competitor for progesterone receptors, administered subcutaneously at 15 mg/kg at days 1, 2, 8 and 15. A reduction in the size of the mammary glands was evident 6 days after the first administration, with complete remission observed after 4 weeks.

Relevance and novel information

To the best of our knowledge, this is the first full report of MFH in a male cat. Although the origin of the progestins responsible for MFH in this case could not be confirmed, in the light of the diagnostic tests performed and the results obtained, accidental contact with hormone-like substances seems to be the only plausible explanation for the cat’s clinical signs. Inhibitor therapy was successful.

INDUÇÃO DE OVULAÇÃO COM SWAB VAGINAL EM GATAS DOMÉSTICAS E SEUS EFEITOS SOBRE A MORFOLOGIA UTERINA

Resumo A ovulação em gatas é induzida por um reflexo neuroendócrino atribuído à estimulação mecânica dos receptores sensoriais durante o coito. Esta estimulação pode ser simulada com auxílio do swab vaginal, desencadeando a pseudogestação. Objetivou-se verificar a eficiência da indução de ovulação com swab, a fim de estabelecer um tratamento contraceptivo natural para felinos domésticos, bem como os efeitos sobre o útero do uso repetido dessa técnica. Na primeira fase do trabalho, foram avaliados 12 animais em três ciclos estrais consecutivos. No primeiro ciclo (T1), houve estimulação vaginal com swab. No segundo ciclo (T2), foi utilizado macho vasectomizado para cópula. No último ciclo (T3), a ovulação foi acompanhada sem estímulo (controle). Na segunda etapa do trabalho, 13 gatas foram submetidas a sucessivos estados de pseudogestação com intuito de verificar os efeitos da estimulação mecânica sobre o útero. A confirmação da ovulação em todas as etapas do trabalho foi realizada por meio da mensuração dos níveis de progesterona. A estimulação vaginal com swab apresentou resposta similar à obtida por monta natural (P>0,05). Algumas gatas apresentaram modificações uterinas discretas; no entanto, nenhum desses achados foi considerado de relevância patológica. Desta forma, a indução de ovulação com swab mostrou-se segura e sem efeitos colaterais expressivos.

Prognostic impact of neoadjuvant aglepristone treatment in clinicopathological parameters of progesterone receptor-positive canine mammary carcinomas

Neoadjuvant treatment of canine mammary carcinomas with the progesterone receptor (PR) antagonist aglepristone has a PR expression-related inhibiting effect on proliferation index (PI). The aim of this study was to evaluate the effect of the treatment in the disease-free period (DFP) and overall survival (OS) of canine mammary carcinomas. Fifty female dogs with mammary carcinomas were treated with aglepristone (n = 34) or oil vehicle (n = 16) before surgery (day 15). PR expression and PI were analysed by immunohistochemistry in samples taken at days 1 and 15. Epidemiological and clinicopathological data were assessed. DFP and OS data were retrieved every 4-6 months for at least 24 months after surgery. Aglepristone treatment increased DFP of animals bearing PR+ tumours with size smaller than 3 cm, complex and mixed tumours, with histologic grades I and II, and with PI ≤ 10%. Although further studies are necessary, current evidence points to treatment with aglepristone as useful for the management of canine mammary tumours.

Progesterone intoxication inducing marked sedation in a cat

A 3-year-old, male castrated domestic shorthair cat presented for sudden onset of severe lethargy and loss of balance a few hours after potentially ingesting capsules containing progesterone. Elevated serum progesterone was confirmed. Supportive care and time resulted in complete resolution of the clinical signs with no long-term complications or recurrence of clinical signs noticed after 1-month follow-up. This is the first description of progesterone intoxication inducing neurological signs in a cat.

Reproduction control in cats: new developments in non-surgical methods

PRACTICAL RELEVANCE

Reproduction control is an area of feline medicine that is assuming increasing importance in companion animal practice. Signs of oestrus such as increased vocalisation, rolling on the ground and a very short interoestrous interval may negatively influence the relationship between cat and owner, and prompt the owner to seek a method of reproduction control. In breeding catteries, control of reproduction may be needed as part of a planned breeding programme.

CLINICAL CHALLENGES

Surgical contraception is not always the owner's wish - especially when a cat may be intended for future breeding. Besides, ethical principles and animal welfare legislation in an increasing number of countries are imposing restrictions on this 'classical approach' to reproduction control. Progestins are routinely used as non-surgical alternatives in cases where fertility is to be preserved, but the associated risks of uterine disease, mammary tumours, fibroadenomatosis or diabetes mellitus have to be taken into account - especially in predisposed animals. Modern, effective pharmacological alternatives are available for managing oestrous suppression and unwanted pregnancy. Detailed knowledge of the physiology of the oestrous cycle in the cat is necessary to ensure that the appropriate treatment is chosen for the individual animal and its owner.

AUDIENCE

This article presents an update for small animal practitioners on these alternative methods; specifically, the use of slow-release GnRH agonists or melatonin implants for hormonal contraception, and the antiprogestin aglepristone for pregnancy termination.

EVIDENCE BASE

Several studies have documented the mode of action and risk of side effects of the traditional alternative to surgical castration - treatment with progestins. Evidence underpinning the safety and efficacy of GnRH agonists and melatonin implants for suppression of fertility in queens and toms is reviewed.

Early detection, aggressive therapy: optimizing the management of feline mammary masses

AIMS

This article reviews the incidence, etiology, diagnosis, treatment and prognosis of mammary tumors in cats.

PRACTICAL RELEVANCE

Approximately 80% of feline mammary masses are malignant, with adenocarcinoma being the most common tumor type. Early diagnosis is, therefore, essential to improve the prognosis and quality of life of affected cats.

TREATMENT APPROACHES

Surgery is the most widely used treatment for malignant tumors. However, as mammary tumors are often advanced and metastasis has already occurred by the time of diagnosis, surgery routinely does not provide a cure. Ovariohysterectomy or hormonal therapy are the treatments of choice for fibroadenomatous hyperplasia (the most common benign mass) and usually lead to a successful outcome.

Induction of abortion with aglepristone in cats on day 45 and 46 after mating

The aim of this study was to test for the efficacy and safety of the use of aglepristone for pregnancy termination on day 45 in cats. Six healthy cats were treated with 10 mg/kg aglepristone sc on day 45 and 46 after mating; six other cats served as untreated controls. The effect of treatment was monitored by general examination, vaginal cytology, ultrasonography and blood sampling for haematology and progesterone determination. Besides, interoestrus interval and next pregnancy including litter size were recorded. The efficacy of treatment was approximately 67% (4/6) with abortion occurring 4-7 days after the first injection and a sanguineous discharge and erythrocytes in vaginal smears for at least 6 days afterwards. The two treated cats that did not abort gave birth to two kittens on day 67 and had a stillbirth of a single kitten on day 71, respectively. As expected enlargement of the mammary glands and lactation were observed in all treated cats. No other treatment-induced side effects were observed. Progesterone levels at abortion were high (30-140 nmol/l), but were decreased on day 55. Aglepristone treatment did not affect fertility in following cycles. Finally, it can be concluded that late-term pregnancy termination with aglepristone is possible but due to a success rate of 67% an ultrasonographical examination 7 days after treatment is an inherent necessity to control the effect of treatment.

Effects of aglepristone, a progesterone receptor antagonist, in a dog with a vaginal fibroma

A 12-year-old, entire, nulliparous crossbreed female dog was presented with a history of vulval bleeding, bulging of the perineum and faecal tenesmus. A firm, non-painful perineal mass, measuring 9.11x5.4 cm, with erythema was detected. Abdominal radiography showed compression and elevation of the rectal ampulla. A dose of 10 mg/kg aglepristone was administered subcutaneously on days 1, 2, 8, 15, 28 and 35. An incision biopsy was taken on day 15 and immunohistochemical analysis showed that the majority of neoplastic cells expressed progesterone receptors. Both the cutaneous erythema and the faecal tenesmus had resolved by day 28. A 50 per cent reduction in size was observed by day 60 (surgical excision). This study shows that benign tumours of the vagina of the dog that contain progesterone receptors can be reduced in size in a palliative or neoadjuvant setting using the progesterone receptor antagonist aglepristone.

Treatment of growth hormone excess in dogs with the progesterone receptor antagonist aglépristone

Acromegaly or hypersomatotropism in dogs is almost always due to progestin-induced hypersecretion of GH originating from the mammary gland. The aim of this study was to investigate whether aglépristone, a progesterone receptor antagonist, can be used to treat this form of canine acromegaly. In five Beagle bitches hypersomatotropism was induced by administration of MPA for over 1 year. Subsequently, aglépristone was administered. Blood samples were collected before MPA administration, immediately before, during, and 3.5 and 5.5 weeks after the last administration of aglépristone for determination of the plasma concentrations of GH and IGF-I. In addition, blood samples for the determination of the 6-h plasma profile of GH were collected before MPA administration, before aglépristone administration, and 1 week after the last aglépristone treatment. MPA administration resulted in a significant increase of the mean plasma IGF-I concentration, whereas analysis of the pulsatile plasma profile demonstrated a trend (P=0.06) for a higher mean basal plasma GH concentration and a higher mean AUC(0) for GH. Treatment with aglépristone resulted in a significant decrease of the mean plasma GH and IGF-I concentrations. Analysis of the pulsatile plasma profile showed a trend (P=0.06) for a lower mean basal plasma GH concentration and a lower mean AUC(0) for GH 1 week after the last aglépristone treatment compared with these values before aglépristone administration. Three and a half and 5.5 weeks after the last aglépristone administration the mean plasma IGF-I concentration increased again. In conclusion, aglépristone can be used successfully to treat dogs with progestin-induced hypersomatotropism.

Mid-gestation pregnancy termination by the progesterone antagonist aglepristone in queens

The efficacy of aglepristone, a progesterone receptor antagonist, to induce abortion on days 25 and 26 after first mating was investigated in queens. The cats were divided into two groups: aglepristone (10 mg/kg, subcutaneously) was injected twice, 24 h apart, on days 25 and 26 after first mating, into group I queens (n = 23). Group II queens (n = 6) were not treated and served as controls. Termination of pregnancy and expulsion of the fetuses were successful in 20 (87%) queens in group I. The mean interval between the first administration of aglepristone and the beginning of vaginal discharge was 5+/-1 days (range 4-7 days) and the mean duration of abortion, defined as time span from first occurrence of vaginal discharge to expulsion of all fetuses observed by ultrasonography was 1 day in nine cats, 2 days in five cats and in five cats, less than 1 day. Treatment failed in three queens. In one queen treatment resulted in birth (66 days after mating) of two vital kittens. In another case, three macerated fetuses were found intrauterine without vaginal discharge. In one cat, two fetuses were expulsed and two remained intrauterine and were born 66 days after last mating. All group II queens gave birth to vital kittens after a normal pregnancy length. The mean serum P4 concentrations were similar in treated and control animals. The results indicate that aglepristone treatment at day 25 of pregnancy could induce abortion in 87% of the treated queens. Itching at the site of injection right after injection was the only side effect noticed and only in one queen.

Comparison of steroid receptor expression in normal, dysplastic, and neoplastic canine and feline mammary tissues

Steroid receptor expression was assessed by immunohistochemistry in neoplastic, hyperplastic/dysplastic, and normal mammary tissue samples removed from 68 queens and 47 bitches, using monoclonal antibodies against human oestrogen-alpha (ER) and progesterone receptors (PR). Mammary lesions were classified according to World Health Organization (WHO) criteria, and all animals with invasive carcinomas were clinically followed for 2 years. Stromal and/or lymphatic invasion and histological grading were also recorded. In both species, ER expression was significantly higher in healthy tissues, hyperplastic/dysplastic lesions, and benign tumours than in carcinomas. The loss of ER expression was more marked in feline than in canine carcinomas. In queens, PR expression increased in dysplastic lesions and "in situ" carcinomas and decreased in invasive carcinomas, even if parts of these tumours were still PR-positive. In bitches no significant variation in PR expression was observed between normal tissue, dysplasias, and benign neoplasms, but was significantly lower in carcinomas. In both species ER and PR expression in invasive carcinomas did not correlate either with histological parameters or overall survival time. This study demonstrates several differences in steroid hormone dependency between the two species. The percentage of PR-positive feline carcinomas suggests a possible role of progesterone in promoting early tumour cell growth in queens. The low percentage of ER-positive invasive carcinomas further demonstrated the aggressive phenotype and behaviour of feline mammary tumours.

Immunohistochemical expression of progesterone receptors, growth hormone and insulin growth factor-I in feline fibroadenomatous change

The immunohistochemical expression, tissue-specific and cell-specific distribution patterns of progesterone receptors (PR), growth hormone (GH) and insulin growth factor-I (IGF-I) have been studied in 22 cases of feline fibroadenomatous change (FFAC). PR and GH were detected in all cases and were distributed homogeneously throughout the lesion, while IGF-I was detected in 77% of the cases at the site of ductal budding. The simultaneous expression of PR, GH and IGF-I was detected in epithelial cells in 14 of 22 cases while PR and GH expression only was detected in epithelial cells in 11 cases. Cases that expressed GH and IGF-I without PR expression in the stroma were the most numerous. Double immunohistochemical staining showed the co-localisation of PR and GH in a subset of ductal epithelial cells located between basal/myoepithelial and luminal cells (probably undifferentiated stem cells). These results suggest that ligand-activated progesterone receptors may induce the local synthesis of GH which in turn may exert its proliferative action directly and also indirectly through the production of other growth factors, such as IGF-I, in an autocrine/paracrine manner.

Follow-up examinations of bitches after conservative treatment of pyometra with the antigestagen aglepristone

The aim of this study was to determine the therapeutic success of the medical treatment of canine pyometra with the antigestagen aglepristone and to document the recurrence rate in relation to the time interval after treatment with antigestagens. In 48 (92.8%) of the 52 treated bitches, healing could be achieved within the first 3 weeks after the treatment had been started. One bitch died as a result of renal insufficiency; in three bitches there was no emptying of the uterus, so ovariohysterectomy became necessary. In these three patients, ovarian and endometrial cysts were present. Forty-one bitches could be followed up for 3 months. Four animals developed a recurrence (9.8%). In three bitches ovarian cysts and cystic endometrial hyperlasia could be found intra operationem. The development of 37 bitches could be followed for at least 1 year. Seven animals developed a pyometra again (18.9%). Two received a repeated treatment with aglepristone and have been free from recurrence for over 12 months. In 37 animals data on the subsequent sex cycles are available. In 22 bitches next heat started at the expected time, in seven animals heat started too early. In eight bitches the period of anoestrus was prolonged. Five of the six bred bitches delivered at least one litter. The presented data show that treatment of pyometra by aglepristone results in a high healing rate. The recurrence rate can be minimized by the selection of bitches without ovarian cysts and cystic endometrial hyperplasia.