Description of the prevalence, histologic characteristics, concomitant abnormalities, and outcomes of mammary gland tumors in companion rats (Rattus norvegicus): 100 cases (1990–2015)

Abstract

OBJECTIVE To describe the prevalence, histologic characteristics, concomitant abnormalities, and outcomes for various types of mammary gland tumors in companion rats (Rattus norvegicus). DESIGN Retrospective case series. ANIMALS 100 client-owned rats. PROCEDURES Medical records of companion rats that had an SC mass and were examined at a veterinary teaching hospital between 1990 and 2015 were reviewed. Information regarding the signalment, age at mass detection, reproductive sterilization status, histologic diagnosis of the SC mass, location of the initial and all subsequent SC masses, treatments administered, and clinical outcomes was extracted from each record and summarized. RESULTS 105 SC masses were initially detected in 100 rats. The most prevalent SC mass identified was mammary gland fibroadenoma (56/105 [53%]), followed by mammary gland carcinoma (13/105 [12%]). Overall, 26 of 105 (25%) masses were malignant. Sexually intact males were more likely to have nonmammary SC tumors than sexually intact females. In rats receiving no adjunctive treatment after excision of a mammary gland fibroadenoma (n = 16), a second fibroadenoma was detected 1 to 8 months after initial excision, at a median of 4.5 months after surgery. A concomitant pituitary gland tumor was identified in most rats with mammary gland fibroadenoma (21/28 [75%]) and other types of mammary gland tumors (10/17 [59%]). Fourteen of 35 (40%) rats with mammary gland fibroadenoma had concomitant reproductive tract abnormalities. CONCLUSION AND CLINICAL RELEVANCE Results suggested that, like other species, companion rats with SC masses should undergo a thorough diagnostic workup that includes histologic examination of the excised mass.

Surgery and electrochemotherapy treatment of incompletely excised mammary carcinoma in two male pet rats (<i>Rattus norvegicus</i>)

“…A recently published study on a large cohort of rats with mammary tumors showed that these neoplasms, independent of the histology type, were more prone to local recurrence than metastasis. Furthermore, the male rats developed malignant tumors rather than benign tumors [16]. Tumor histology results and the observed aggressive biological characteristics are consistent with mammary carcinoma diagnosed for the described cases.…”

“…Tumor histology results and the observed aggressive biological characteristics are consistent with mammary carcinoma diagnosed for the described cases. The extensive nature of the lesions prevented large excision, resulting in incomplete tumor removal and thereby exposing the patients to risk of recurrence, as reported in literature [16]. Due to the extreme rarity of this malignant neoplasm in male rats and considering scant reports of chemotherapy in pet mice and rats, the two rats were treated by loco-regional injection of cisplatin to the tumor bed.…”

Sarcoma indiferenciado espontâneo em Rattus norvegicus concomitante com parasitismo por Hymenolepis sp. – relato de caso / Spontaneous undifferentiated sarcoma in Rattus norvegicus concomitant with parasitism by Hymenolepis sp. – case report

“…A neoplasia de maior prevalência em ratas fêmeas é o fibroadenoma mamário (TROTTE et al, 2008;VERGNEAU-GROSSET et al, 2016;ALCÂNTARA et al, 2019;BARBOSA, 2019), o que não torna incomum a aparição de outras formações em diferentes localizações como foi comprovado por Bomhard & Rinke (1994). Neste estudo foram analisados os tumores espontâneos de 2520 Wistar, sendo 1270 fêmeas das quais pôde ser observado o útero de 1236 e 146 (11,8%) delas possuíam neoplasias no órgão, o que mostra que neoplasias uterinas em ratas são recorrentes.…”

“…Os hormônios envolvidos no ciclo estral são os principais promotores dos tumores uterinos e mamários, sendo que a prolactina está diretamente relacionada às neoplasias de mama e, o aumento da proporção estradiol:progesterona, ao longo de vários ciclos, pode culminar em neoplasia uterina, já que o estrogênio tem efeito trófico no endométrio (HARLEMAN et al, 2012). Somado a isso, Vergneau-Grosset et al (2016) notaram que as ratas castradas possuíam três vezes menos riscos de desenvolverem neoplasias mamárias.…”

Companion rats (Rattus norvegicus) with cutaneous lesions: a retrospective study of 470 cases at two university veterinary teaching hospitals (1985–2018)

“…It is possible that some of the undiagnosed masses were mammary tumours. Rats have six pairs of mammary glands (three thoracic, one abdominal and two inguinal) that extend from the neck to the inguinal region and mammary neoplasia is common . However, tumours with a specific diagnosis of mammary neoplasia were excluded from this study because mammary tumours are not actually skin tumours — in addition, they were the subject of a previous substantial report …”