Vaginal leiomyoma in a goat expressing the nuclear progesterone receptor (PGR): a case report.

BACKGROUND: The risk of developing tumorous diseases in the genital tract also increases with age in animals. One of the classified tumor types is genital leiomyoma. Presently, our understanding of the pathogenesis of this tumor in goats is, however, limited. This accounts also for the information regarding the presence of steroid hormone receptors and, thus, possible responsiveness to circulating steroids. CASE PRESENTATION: This study describes the case of a vaginal tumor in a seven-year-old Anglo-Nubian goat. The goat was presented due to blood mixed vaginal discharge. Per vaginal examination a singular pedunculated mass in the dorsum of the vagina measuring approximately 3 cm x 4 cm x 4 cm was revealed. After administering epidural anesthesia, the mass was removed electrothermally. There were no postoperative complications. The histopathological examination identified the mass as a leiomyoma. The immunohistochemical examination revealed the presence of the nuclear progesterone receptor (PGR) in the tumor tissue. One year after the surgery, during the follow-up examination, the goat was in good overall health, and the owners had not observed any recurrence of vaginal discharge. CONCLUSIONS: When observing vaginal discharge in goats, it is important to consider the possibility of genital tract tumors. These tumors may express sex steroid receptors. In the future, it is worth considering the investigation of potential approaches for preventing tumorigenesis or treating the tumor, such as castration or the administration of antiprogestogens.

An exploratory study on the prevalence of neoplasms in two strains of laying hens during an extended production cycle.

There is a trend towards extended periods of lay in the laying hen industry. Extended cycles without a moulting stage gives the opportunity to obtain more eggs from a single hen. However, appropriate management and care for older laying hens is needed. In this trial we assessed the prevalence of conditions in old laying hens with a focus on neoplastic diseases. In total 150 ISA Brown and 150 Dekalb white laying hens were selected at 86 weeks of age. Of each hen line, 75 hens were necropsied at 86 weeks of age; the other half were monitored for 44 weeks after which they were necropsied. At week 86, 15.3% of the hens suffered from a neoplasm, ISA Brown being the most affected. During the follow up period, 50 birds died because of a natural cause of which 20 hens showed signs of a neoplasms. At the end of the follow up period, 43% of the hens were affected by a neoplasm. Adenocarcinoma was the most prevalent neoplasm and equally distributed among both hen lines. Leiomyomas were most frequently observed in ISA brown hens. Among causes of death, 19.05% of ISA brown and 20.69% of Dekalb White was attributed to a neoplasm. Furthermore, link with ovarian activity and other pathologies were made with significant correlations between adenocarcinomas and inactive ovaries. In conclusion, this study shows that the prevalence of adenocarcinoma and leiomyoma is a factor to be considered in longer laying cycles with 1/5th of the mortality caused by these processes.RESEARCH HIGHLIGHTSAt 86 weeks of age, the prevalence of neoplasms was 15.3%, mainly in brown hens.At 130 weeks of age, 43% of the hens were affected by a neoplasm.Adenocarcinoma was the most prevalent neoplasm equally distributed among hen lines.Leiomyoma was the second most prevalent neoplasm, mainly found in brown hens.

Ultrasonographic Appearance of Gallbladder Neoplasia in 14 Dogs and 1 Cat.

Ultrasonography is the most commonly used diagnostic imaging tool for gallbladder disease in veterinary medicine. Primary gallbladder neoplasia is an uncommon finding with variable prognosis for which no studies have been published describing their ultrasonographic appearance and diagnosis. This retrospective, multicenter, case series study examines the ultrasonographic appearance of gallbladder neoplasia with histologically or cytologically confirmed diagnoses. A total of 14 dogs and 1 cat were analyzed. All discrete masses were sessile in shape and varied in size, echogenicity, location, and gallbladder wall thickening. All studies with images showing Doppler interrogation exhibited vascularity. Cholecystoliths were an uncommon finding, being present in only one case in this study, unlike in humans. The final diagnosis of the gallbladder neoplasia was neuroendocrine carcinoma (8), leiomyoma (3), lymphoma (1), gastrointestinal stromal tumor (1), extrahepatic cholangiocellular carcinoma (1), and adenoma (1). Findings from this study indicate that primary gallbladder neoplasms have variable sonographic appearances and cytologic and histologic diagnoses.

CT features of gastrointestinal spindle cell, epithelial, and round cell tumors in 41 dogs.

There is sparse published information on computed tomographic (CT) characteristics of canine gastrointestinal tumors. The purposes of this multi-center, retrospective, descriptive study were to describe the CT features of histologically-confirmed canine gastrointestinal spindle cell, epithelial, and round cell tumors and, when available, describe the corresponding ultrasound findings. The inclusion criteria were as follows: availability of pre-and post-contrast CT study, and a histopathological diagnosis of the lesions. Recorded parameters were tumor size, location, gastrointestinal wall layers involvement, lesion's growth and enhancement patterns, tumor margination, presence of stenosis, mineralization, ulcerations, lymphadenopathy, or other lesions in the abdomen/thorax. When available, ultrasound images were evaluated. Forty-one dogs met the inclusion criteria and had the following histological diagnoses: 21/41 (51%) spindle cells (7 leiomyomas, 14 leiomyosarcomas/gastrointestinal stromal tumors (GISTs)), 13/41 (32%) epithelial (adenocarcinoma), and 7/41 (17%) round cell (lymphoma) tumors. The growth pattern was concentric, eccentric, and mixed in epithelial, spindle cell, and round cell tumors, respectively. Spindle cell tumors had the largest main volume and involved the outer gastrointestinal layer with an unaffected inner layer. Leiomyosarcomas/GISTs showed irregular margins compared to leiomyomas. Only lymphomas showed multifocal gastrointestinal involvement. Nine carcinomas and six spindle cell tumors caused partial stenosis with secondary sub-obstruction. Mineralizations were more frequent in spindle cell tumors (10/21) and absent in lymphomas. Lymphadenomegaly was widespread in lymphomas, regional in leiomyosarcomas-GISTs and adenocarcinomas, and absent in leiomyomas. The reported CT features may be useful in prioritizing the differential diagnosis between spindle cell, epithelial, and round cell tumors, similar to those reported on ultrasound.

Canine smooth muscle tumors: A clinicopathological study.

Canine smooth muscle tumors (SMTs) commonly develop in the alimentary and female genital tracts and less frequently in soft tissue. The definition of histological criteria of malignancy is less detailed for SMTs in dogs than in humans. This study evaluated the clinicopathologic features of canine SMTs and compared the veterinary and human medical criteria of malignancy. A total of 105 canine SMTs were evaluated histologically and classified according to both veterinary and human criteria. The Ki67 labeling index was assessed in all SMTs. Estrogen receptor (ER) and progesterone receptor (PR) expression was evaluated for soft tissue SMTs. Follow-up data were available in 25 cases. SMTs were diagnosed in the female genital tract (42%), alimentary tract (22%), and soft tissue (20%). Soft tissue SMTs frequently arose in the perigenital area, pelvic cavity, and retroperitoneum. A subset of soft tissue SMTs expressed ER and/or PR, resembling the gynecologic type of soft tissue SMT in humans. SMTs were less frequently malignant when assessed with human criteria than with veterinary criteria, better reflecting their benign behavior, especially in the genital tract where human criteria tolerate a higher mitotic count for leiomyoma. Decreased differentiation was correlated with increased proliferation, necrosis, and reduced desmin expression. Mitotic count, Ki67 labeling index, and necrosis were correlated with metastases and tumor-related death. Further prognostic studies are warranted to confirm the better performance of the human criteria when assessing SMT malignancy, especially genital cases, to confirm their usefulness in ER/PR-expressing soft tissue SMTs, and to better define the most useful prognostic parameters for canine SMTs.

Reproductive tract neoplasia in adult female Asian elephants (Elephas maximus).

Recent reports have highlighted a lower-than-expected prevalence of neoplasia in elephants and suggested mechanisms for cancer resistance. But despite infrequent reports in the literature, uterine neoplasia is common in managed Asian elephants (Elephas maximus). This study is an archival review of reproductive tract neoplasia in 80 adult female Asian elephant mortalities in managed care facilities in the United States from 1988 to 2019. Neoplasms occurred in 64/80 (80%) of cases. Most were in the uterus (63/64; 98%) with only a single case of ovarian neoplasia. Myometrial leiomyomas were present in 57/63 (90%) cases with uterine neoplasia. Uterine adenocarcinoma was present in 8/63 (13%) cases. Remaining cases included endometrial adenoma (2), focal carcinoma in situ in endometrial polyps (1), anaplastic carcinoma (1), endometrial hemangioma (1), primitive neuroectodermal tumor (PNET; 1), and angiosarcoma (1). One case with uterine adenocarcinoma had a separate pelvic mass histologically characterized as an anaplastic sarcoma. Distant metastases were documented in 5/8 (63%) cases of uterine adenocarcinoma, and in the uterine anaplastic carcinoma, PNET, and angiosarcoma. Four uterine adenocarcinomas and one carcinoma in situ were examined immunohistochemically for pan-cytokeratin, vimentin, and estrogen receptor. In all, neoplastic cells were pan-cytokeratin positive and vimentin negative, and in 2 cases were immunoreactive for estrogen receptor. Results show that female reproductive tract neoplasia, particularly of the uterus, is common in Asian elephants and is not limited to leiomyomas. Importantly, uterine neoplasms have the potential to impact fecundity and may represent obstacles to conservation in managed care.

Progesterone-responsive vaginal leiomyoma and hyperprogesteronemia due to ovarian luteoma in an older bitch.

BACKGROUND: This is the first report about a vaginal leiomyoma concomitant with an ovarian luteoma in a bitch. CASE PRESENTATION: A 11-year-old intact female Labrador retriever was referred because of anuria, constipation and protrusion of a vaginal mass through the vulvar commissure. The bitch had high serum progesterone concentration (4.94 ng/ml). Because of the possibility of progesterone responsiveness causing further increase of the vaginal mass and since the bitch was a poor surgical candidate a 10 mg/kg aglepristone treatment was started SC on referral day 1. A computerized tomography showed a 12.7 × 6.5 × 8.3 cm mass causing urethral and rectal compression, ureteral dilation and hydronephrosis. A vaginal leiomyoma was diagnosed on histology. As serum progesterone concentration kept increasing despite aglepristone treatment, a 0.02 ng/mL twice daily IM alfaprostol treatment was started on day 18. As neither treatment showed remission of clinical signs or luteolysis, ovariohysterectomy was performed on referral day 35. Multiple corpora lutea were found on both ovaries. On histology a luteoma was diagnosed on the left ovary. P4 levels were undetectable 7 days after surgery. Recovery was uneventful and 12 weeks after surgery tomography showed a reduction of 86.7% of the vaginal mass. The bitch has been in good health and able to urinate without any complication ever since. CONCLUSIONS: This case demonstrates the importance of identifying progesterone related conditions as well as the importance of judiciously using a combined medical and surgical approach.

Gastric leiomyoma in a sea bass Dicentrarchus labrax broodfish.

This report describes a spontaneously arising non-infiltrative neoplasm of gastric tunica muscularis in a broodstock sea bass Dicentrarchus labrax from an Italian aquaculture farm. Microscopically, the mass was circumscribed and non-encapsulated and was composed of spindle cells arranged in parallel interlacing bundles or, occasionally, a whirling pattern. Cells had a small quantity of eosinophilic cytoplasm with distinct cell borders. Neoplastic cells were immuno-reactive with smooth muscle actin, vimentin and desmin; S100 was negative. The mucosal epithelium was intact with no neoplastic involvement. A gastric leiomyoma was diagnosed based on the findings. More efforts should be made to study the possible etiology of leiomyoma affecting fish from aquaculture.

Testicular leiomyoma and spermatogenic failure syndrome in a seabass from broodstock.

Testicular leiomyomas and gonadal dysfunctions are not commonly reported in teleost and particularly in broodstock fish. In the present work, a testicular leiomyoma related to an unusual case of spermatogenic failure syndrome, in a broodstock seabass coming from an Italian aquaculture farm, is reported. At gross pathology, the circumscribed neoplasia showed several white nodular masses, originating from the gonad, deforming the anatomo-physiological shape. From light microscopy, the presence of neoplastic tissue islands with spindle cells with a whirling pattern and the low presence of connective tissue were evident and originated from smooth muscle cells. Seminiferous tubules showed severe azoospermia with the absence of sperm cells even closer to the neoplastic area. Immunohistochemical analysis was positive for alpha-SMA, desmin and vimentin but negative for S-100, confirming a diagnosis of leiomyoma. This is the first report of spermatogenic failure syndrome associated with a testicular leiomyoma in fish from broodstock. More efforts should be made in studying broodstock fish pathologies related to fish maintenance and hormonal treatments that could economically affect aquaculture production.

Outcomes associated with vaginectomy and vulvovaginectomy in 21 dogs.

OBJECTIVE: To report the outcomes of dogs with lesions of the genitourinary tract treated by vaginectomy or vulvovaginectomy. STUDY DESIGN: Multi-institutional retrospective study. ANIMALS: Female dogs that underwent vulvovaginectomy, complete vaginectomy, or subtotal vaginectomy from 2003 to 2018 with complete medical records and a minimum of 60 days follow-up. METHODS: Data collected from medical records included preoperative, intraoperative, and postoperative data, such as the occurrence of urinary incontinence (UIC), disease recurrence, and death/euthanasia. RESULTS: This study included 21 dogs. Four dogs had vulvovaginectomy, six had complete vaginectomy, and 11 had a subtotal vaginectomy performed. The mean age at surgery was 9.2 years (SD, 3.3). Thirteen dogs were intact at presentation. Smooth muscle tumors were diagnosed most commonly (10 leiomyomata, three leiomyosarcomas, two leiomyofibromas). The median duration of follow-up was 520 days (range, 71-1955). Major complications requiring revision surgery were recorded in two dogs. Postoperative UIC occurred in six of 21 dogs, resolving spontaneously within 60 days in three dogs. Dogs with malignant tumors (n = 6) survived at least 71 days (median, 626; 95% CI, 71-1245), and recurrence of disease occurred in two dogs. In dogs with benign tumors (n = 15), the median survival time was not reached. These dogs survived at least 104 days and had no recurrence of the disease. CONCLUSION: Vaginectomy and vulvovaginectomy resulted in prolonged survival and low rates of major complications and UIC. CLINICAL SIGNIFICANCE: This study provides evidence to recommend that the risks of this procedure and expectations should be discussed with clients.

Contrast-enhanced computed tomography may be helpful for characterizing and staging canine gastric tumors.

In humans, computed tomography (CT) is a widely performed technique for the diagnosis and staging of gastric tumors. The purpose of this retrospective case series study was to describe CT findings in a group of dogs with confirmed gastric tumors. For each included dog, the following CT parameters were recorded: gastric tumor location, tumor shape, gastric involvement pattern, tumor enhancement pattern in early and late phases, presence and location of lymphadenopathy, gastric tumor attenuation values, attenuation values of enlarged lymph nodes, maximum short-axis diameter (mm) of enlarged lymph node, maximum long-axis diameter (mm) of enlarged lymph node, and short-axis diameter to long-axis diameter ratio (short axis/long axis). A total of 16 dogs met inclusion criteria and had the following final diagnoses: five lymphoma, six adenocarcinoma, three inflammatory polyps, and two leiomyoma. In the early- and delayed-phase postcontrast images, the mean CT attenuation value for lymphoma was lower than that of other gastric tumors. Lymphadenopathy was widespread in lymphomas and regional in adenocarcinomas. Lymphadenopathy was not detected in leiomyomas. Lymph node measurements in lymphoma were larger than lymph node measurements in adenocarcinoma. Although there were overlapping findings for the different types of gastric tumors, contrast-enhanced CT provided helpful information for characterizing gastric tumors based on the following criteria: early and late enhancement patterns, the site of origin of the mass lesion, and extent of local invasion and distant metastases. Lymphoma should be considered for canine gastric tumors with low mean attenuation values during early- and delayed-phase postcontrast images, and widespread, bulky, and rounded lymphadenopathy.

Characterization of an Unusual Mesenchymal Tumor in the Proventriculus of a Free-ranging Red-tailed Hawk (Buteo jamaicensis).

An adult, female red-tailed hawk (Buteo jamaicensis) was presented for examination after being found unable to fly on a private citizen's property. Further diagnostic testing revealed a vascular, soft tissue mass arising from the serosal surface of the proximal proventriculus. Postmortem histological and immunohistochemical examination of the mass revealed an unusual mesenchymal tumor with features consistent with a leiomyoma or low-grade gastrointestinal stromal tumor.

Massive uterine lipoleiomyoma and leiomyoma in a miniature poodle bitch.

A 15-year-old, intact, female miniature poodle was presented for further evaluation of a large abdominal mass. Computed tomography was conducted to determine the origin of the mass and 2 large uterine masses were discovered. Ovariohysterectomy was performed and histopathological evaluation revealed a massive uterine lipoleiomyoma (27 × 17 × 15 cm), the largest recorded in the veterinary literature, and a smaller leiomyoma (7 × 5 × 4 cm).

Lipoléiomyome utérin massif et léiomyome chez une chienne Caniche miniature. Une chienne Caniche miniature intacte âgée de 15 ans a été présentée pour une évaluation approfondie d'une grosse masse abdominale. Une analyse par tomodensitométrie a été réalisée afin de déterminer l'origine de la masse et deux grandes masses utérines ont été découvertes. L'ovariohystérectomie a été réalisée et l'évaluation histopathologique a révélé un lipoléimomyome utérin massif (27 × 17 × 15 cm), le plus gros jamais consigné dans la littérature vétérinaire et un plus petit léiomyome (7 × 5 × 4 cm).(Traduit par Isabelle Vallières).

SURGICAL MANAGEMENT OF UTERINE LESIONS IN TWO CAPTIVE ORANGUTANS ( PONGO SPP.).

Uterine lesions in two orangutans were effectively managed with surgical intervention. A 26-year-old hybrid orangutan ( Pongo spp.) was diagnosed with uterine adenomyosis based on advanced imaging. Histologic evaluation identified multifocal myometrial endometriosis, a variant of adenomyosis. A 27-year-old Bornean orangutan ( Pongo pygmaeus) was diagnosed with a focal uterine fibroid based on histologic examination. The animals were housed at separate institutions and initially presented with dysmenorrhea and menorrhagia. Both animals were treated intermittently for episodes of dysmenorrhea, with recurrence of clinical signs after each treatment. Due to the lack of consistent response to medical management, an ovariohysterectomy in the hybrid orangutan and a myomectomy in the Bornean orangutan were performed and resulted in complete resolution of clinical signs. Surgical management of adenomyosis and neoplasia has previously been reported in nonhuman primates. These cases are the first known documentation of surgical management of multifocal myometrial endometriosis and a fibroid in orangutans.

Immunoexpression of Steroid Hormone Receptors and Proliferation Markers in Uterine Leiomyoma and Normal Myometrial Tissues from the Miniature Pig, Sus scrofa.

Uterine leiomyomas in miniature pet pigs occur similarly to those in women with regard to frequency, age, parity, and cycling. Clinical signs, gross, and histologic features of the porcine tumors closely resemble uterine leiomyomas (fibroids) in women. Although fibroids are hormonally responsive in women, the roles of estrogen and progesterone have not been fully elucidated. In this study, immunohistochemistry was used to assess the expression of the steroid hormone receptors, estrogen receptor alpha (ER-α), estrogen receptor beta (ER-ß) and progesterone receptor (PR), and cell proliferation markers, proliferating cell nuclear antigen (PCNA) and Ki-67 in tumor and matched myometrial tissues sampled from miniature pigs. A "quickscore" method was used to determine receptor expression and labeling indices were calculated for the markers. ER-α/ß and PR were localized to the nuclei of smooth muscle cells in both tissues. PR expression was intense and diffuse throughout all tissues, with correlation between tumors and matched myometria. Conversely, ER-α expression was variable between the myometrial and tumor tissues, as well as between animals. ER-ß expression was low. PCNA and Ki-67 were localized to the nucleus and expression varied among tumors; however, normal tissues were overall negative. These findings support further investigation into the use of the miniature pig as a model of fibroids in women.

Endoscopic-assisted resection of a pedunculated uterine leiomyoma with maximal tissue preservation in a cow and a mare.

OBJECTIVE: To report successful minimally invasive treatment of a uterine leiomyoma in a cow and a mare. STUDY DESIGN: Clinical report. ANIMAL POPULATION: Limousine cow (n = 1), Thoroughbred mare (n = 1). METHODS: A 10-year-old cow and an 18-year-old mare were presented for difficulties in breeding and infertility, respectively. Examination of the reproductive tract revealed the presence of a large mass attached to the uterine wall via a wide and short peduncle in both cases. The mass expanded into the uterine lumen in the mare and into the abdomen in the cow. Both masses were removed using a minimally invasive endoscopic approach and a vessel-sealing and dividing device. RESULTS: Minimally invasive surgical resection of a subserosal and a submucosal leiomyoma with maximal sparing of uterine tissue resulted in a short convalescence period and apparent return to breeding function in a cow and a mare. Use of a vessel-sealing and dividing device provided excellent hemostasis and decreased tissue handling. CONCLUSION: Leiomyoma with short, wide, and thick peduncles were treated successfully in a cow and a mare with minimally invasive endoscopic approaches aiming at maximal uterine tissue preservation.

ULTRASONOGRAPHIC FEATURES OF CANINE GASTROINTESTINAL STROMAL TUMORS COMPARED TO OTHER GASTROINTESTINAL SPINDLE CELL TUMORS.

Canine gastrointestinal stromal tumors (GISTs) are a recent subtype of gastrointestinal spindle cell tumor recognized with the increasing use of immunohistochemistry. To our knowledge, no imaging features have been described in immunostochemically confirmed canine GISTs. The objective of this retrospective, cross-sectional study was to describe ultrasonographic features of canine GISTs compared with other spindle cell tumors. Thirty-seven dogs with an ultrasonographically visible gastrointestinal mass and a histopathologic diagnosis of spindle cell neoplasia were examined. Immunohistochemistry staining was performed for retrieved tissue samples to further differentiate the tumor type and each sample was interpreted by a single veterinary pathologist. Ultrasonographic features recorded examined included mass echogenicity, homogeneity, presence of cavitation, layer of origin, bowel wall symmetry, and loss of wall layering, location, size, vascularity, and evidence of perforation or ulceration. Tumor types included 19 GISTs, eight leiomyosarcomas, six leiomyomas, and four nonspecified sarcomas. Gastrointestinal stromal tumors were significantly more likely to be associated (P < 0.03) with abdominal effusion than other tumor types. There was overlap between the anatomical locations of all tumors types with the exception of the cecum where all eight tumors identified were GISTs. Besides location, there were no unique ultrasound features of GISTs that would allow distinction from other gastrointestinal spindle cell tumors. Similar to previous studies, GISTs appeared to be the most common spindle cell tumor associated with the cecum in our sample of dogs. The high frequency of abdominal effusion with GIST's was of unknown etiology could possibly have been due to septic peritonitis.

MEDICAL MANAGEMENT OF LEIOMYOMATA AND SUSPECTED ENDOMETRIOSIS IN AN ALLEN'S SWAMP MONKEY (ALLENOPITHECUS NIGROVIRIDUS).

A 13-yr-old female nulliparous Allen's swamp monkey (Allenopitchecus nigroviridis) presented with intermittent excessive vaginal bleeding, cyclical lethargy, and a history of irregular menstrual cycles. Abdominal ultrasonography revealed a subjectively thickened, irregular endometrium, multiple leiomyomata (uterine fibroids), and bilateral anechoic foci on the ovaries. Treatment was initiated with leuprolide acetate i.m. monthly for 6 mo. Recheck ultrasound at 3 mo showed a decrease in leiomyoma diameter and no evidence of active follicles on the ovaries. Eleven months following completion of treatment, clinical signs recurred and the animal was treated with a deslorelin implant. Since implant placement, no vaginal bleeding has been noted.

Canine vaginal leiomyoma diagnosed by CT vaginourethrography.

A 13 yr old female spayed Labrador retriever presented for vulvar bleeding. Abdominal radiographs revealed a soft tissue mass in the ventral pelvic canal. A computed tomography (CT) exam and a CT vaginourethrogram localized the mass to the vagina, helped further characterize the mass, and aided in surgical planning. A total vaginectomy was performed and the histologic diagnosis was leiomyoma. Vaginal tumors make up 1.9-3% of all tumors. Seventy-three percent of vaginal tumors are benign, and 83% of those are leiomyomas. Leiomyomas often have a good long-term prognosis with surgical resection. The diagnostic investigation of this case report utilized a multimodal imaging approach to determine the extent and respectability of the vaginal mass. To the best of the authors' knowledge, this is the first report describing a CT vaginourethrogram.

Validation of the aging hen (Gallus gallus domesticus) as an animal model for uterine leiomyomas.

Uterine leiomyomas, or fibroids, are the most frequent gynecological tumors in premenopausal women with as many as 65% of women becoming clinically symptomatic. Uterine fibroids are benign myometrial tumors that produce large quantities of extracellular matrix proteins. Despite its high morbidity, the molecular basis underlying the development of uterine leiomyomas is not well understood. Domestic hens of Gallus gallus domesticus develop oviductal leiomyomas similar to those found in humans. We investigated the natural history of chicken leiomyomas, in vivo expression of protein biomarkers, and in vitro expression of ovarian steroid receptors. Based on the analysis of 263 hens, tumor prevalence, tumor number per hen, and tumor size increased as the hens aged. Immunohistochemistry for alpha-smooth muscle actin (SMA) and desmin confirmed the smooth muscle phenotype of the chicken leiomyomas. Intense collagen expression was detected in these oviductal leiomyomas by Mason's trichrome, and the tumors also showed increased expression of TGFB3 and collagen type I mRNAs. Consistent with human leiomyomas, chicken fibroids displayed increased BCL2 and estrogen (E) and progesterone (P) receptor expression. Chicken leiomyomas were dissociated for in vitro culture. Cells from explants were positive for SMA, desmin, and E and P receptors until the fourth passage. These cells also displayed a response similar to human cells when challenged with halofuginone, an antifibrotic agent. Our findings indicate that the chicken is an excellent complementary model for studies involving the pathophysiology of human uterine leiomyomas.