Uterine Smooth Muscle Tumors in Potbellied Pigs (Sus scrofa) Resemble Human Fibroids: A Potential Animal Model

Abstract

Uterine leiomyomas, commonly termed fibroids, clinically affect approximately 25% of women of reproductive age in the United States, with a subclinical incidence as high as 77%. The pathogenesis of fibroid formation remains poorly understood, due in large part to the lack of a suitable animal model. This retrospective study characterizes the clinical, gross, and histopathologic features of similar, spontaneously occurring uterine tumors in potbellied pigs. Medical records available through a local Potbellied Pig Spay/Neuter Program, pig sanctuaries, and the Duchess Fund database were reviewed for evidence of reproductive disease or surgery. One-hundred and six female potbellied pigs were evaluated and uterine neoplasia was identified in 17 animals; tissues were available for 13 of these. Uterine leiomyoma was diagnosed in 11 of 13 cases, leiomyosarcoma in 1 of 13 cases, and undifferentiated sarcoma in 1 case. Pigs presented with clinical signs including abdominal distension or vaginal bleeding or were subclinical and identified during ovariohysterectomy. Tumors ranged from microscopic to 45 kg, were often multiple, and primarily involved the uterine horns. Hematoxylin and eosin and trichrome-stained sections were evaluated for morphological features of human and animal leiomyomas; immunohistochemistry to detect smooth muscle actin was also performed. The cellular pattern/morphology and variable degree of fibroplasia of the leiomyomas were similar to that reported for human fibroids. These results support further investigation of uterine leiomyomas in potbellied pigs as a potentially valuable animal model for studying human fibroids.

Comparison of Human and Rat Uterine Leiomyomata: Identification of a Dysregulated Mammalian Target of Rapamycin Pathway

“…Models have been published in several species, including mouse (4-6), rat (7), guinea pig (8)(9)(10), and potbellied pig (11). The Eker rat, first described in 1954 as a rodent model of renal cell carcinoma, was subsequently observed to develop spontaneous uterine leiomyomata in f65% of female rats by 16 months of age (12,13).…”

Pathology in Practice

“…2,3 However, on the basis of the diagnostic criteria for human myometrial tumors 4 and reported features of myometrial tumors in potbellied 2 or miniature pigs, 3 the increased cell density of the myometrial leiomyoma in the pig of this report-plus the absence of coagulative necrosis of neoplastic cells and mitotic index < 1 mitotic figure/10 hpfs-is reminiscent of the cellular variant of human myometrial leiomyoma.…”

Validation of the Aging Hen (Gallus gallus domesticus) as an Animal Model for Uterine Leiomyomas1

“…Leiomyomas of the reproductive tract occur in several species of domestic animals, including the potbellied pig [49], the quail [50], and the German Shepherd dog [51], and nondomestic animals such as the otter [52], seal [53], cheetah [54], white rhinoceros [55], elephant [56], and crab-eating macaque [57]. Although the high incidence of uterine fibroids and their associated clinical problems are significantly important among reproductive aged women, the molecular basis for the initial myocyte transformation and growth of these tumors remains unknown.…”