Tumors and Tumor-like Lesions in the Mammary Gland of 24 Pet Rabbits

Abstract

The aim of this retrospective study (2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011) was to examine mammary tumors and tumor-like lesions in 24 pet rabbits by histopathology and immunohistochemistry. Rabbits were aged 2 to 8 years. Seventeen were female and 7 female-spayed. Diagnosed tumor-like lesions were lobular hyperplasia (2 rabbits) and multiple cysts (10 rabbits). Tumors included cystadenoma (7 tumors; 3 rabbits), intraductal papilloma (2 tumors; 1 rabbit), intraductal papillary carcinoma (1 tumor), adenocarcinoma (14 tumors; 13 rabbits), adenosquamous carcinoma (2 tumors; 2 rabbits), and matrix-producing carcinoma (1 tumor). The most frequently diagnosed lesion was invasive carcinoma (n ¼ 17). Ten rabbits had several lesions. Immunohistochemistry for calponin and p63 showed that the diagnosed tumor-like lesions, benign tumors, and noninvasive carcinoma had a peripheral myoepithelial layer that was lacking in the invasive carcinomas. In 13 of 14 (93%) of the invasive carcinomas, however, there were variable numbers of calponin-and/or p63-immunopositive cells ranging from 0.1% to 40% with morphological features of either retained nonneoplastic myoepithelial cells or neoplastic epithelial cells with a myoepithelial differentiation. Tumor recurrence was reported in the rabbit with the matrix-producing carcinoma and in 3 rabbits with mammary adenocarcinomas displaying !20 mitotic figures in 10 high-power fields and high numbers of neoplastic cells with a myoepithelial differentiation (19%-39%). The rabbit with the matrix-producing mammary carcinoma developed cutaneous metastases confirmed by histopathology. This study shows that different types of mammary tumor-like lesions and tumors can occur in pet rabbits. Keywords immunohistochemistry, mammary gland, tumors and tumor-like lesions, myoepithelial cells, rabbitThe most common tumor of the rabbit (Oryctolagus cuniculus) is the uterine adenocarcinoma, 20 whereas mammary tumors and tumor-like lesions are rarely reported in pet and laboratory rabbits. In a study of uterine disorders in 59 rabbits, the concurrent presence of a uterine and a mammary gland adenocarcinoma was observed in 4 rabbits, 2 of which had endometrial hyperplasia as well. 28 In another investigation of 47 rabbits with uterine disorders, mammary gland disease including cystic lesions was diagnosed in 15 of these rabbits by physical examination. 24Histopathological features of neoplastic and nonneoplastic proliferative lesions of the mammary gland of rabbits are described in only a few publications that relate to laboratory rabbits. 11,26 In a breeding colony of rabbits, most invasive and noninvasive neoplasms developed in mammary glands with preexisting cystic disease.11 A cystic mammary adenocarcinoma was diagnosed in a 44-month-old female nulliparous New Zealand White laboratory rabbit with concurrent mammary hyperplasia and dysplasia and elevated prolactin levels due to a pituitary adenoma. 26 To the authors' knowledge, a detailed histopathological and immunohistochemical character...

Tumor Infiltrating Lymphocytes in Pet Rabbit Mammary Carcinomas: A Study with Relevance to Comparative Pathology

“…Histological parameters extracted from the databases were the tumor area with a tubular growth pattern in percent of the entire tumor area, the mitotic count per ten 40× high power fields (HPFs) under consideration of the field number of the microscope, the degree of nuclear pleomorphism, as well as the degree of tumor invasion [10,11,15]. The results of the former three parameters were used to determine the histological tumor grade [32][33][34].…”

“…The results of the former three parameters were used to determine the histological tumor grade [32][33][34]. Depending on the degree of tissue infiltration, tumors were classified as those with mild, moderate, or marked invasive behavior [10,11,15]. Necrosis was recorded as minimal, mild, moderate, and marked, if it affected <10%, 10-39%, 40-69%, and ≥70% of the tumor area, respectively [10].…”

“…Since majority of rabbit mammary carcinomas are ERα and PR negative, the rabbit has been proposed as a potential animal model for ERα/PR negative breast cancer in humans [10] as well as potentially also for triple negative human breast carcinomas [12]. In addition, rabbits may be a suitable model for breast cancer types with a myoepithelial differentiation of tumor cells and a prolactin-associated tumorigenesis as well [10][11][12]15].…”

“…It has been shown that most rabbit mammary tumors are carcinomas, i.e., 50-98% depending on the respective study, the majority of these being adenocarcinomas [10][11][12]15,16]. Recent investigations on rabbit mammary carcinomas analyzed in detail the histological features [10,15,16], estrogen and progesterone receptor status [10], as well as the intra-tumoral presence of retained non-neoplastic myoepithelial cells and tumor cells with a myoepithelial differentiation [11,15]. Definitive prognostic factors are not available yet, and currently the only therapeutic option is surgical excision [12].…”

Expression of Myoepithelial Markers in Mammary Carcinomas of 119 Pet Rabbits

“…The reported incidence of this tumor in 2–3 years old does is 4%, whereas about 80% of 5–6 years old does are affected [2]. There is an increasing recognition of mammary tumors in pet rabbits [3,4,5]. All tumors with reported sex of the patient occurred in female or female-spayed rabbits [3,4,5], and 67–98% of the tumors were carcinomas [3,4,5].…”