Clinicopathological Diversity of Canine Mammary Gland Tumors in Sri Lanka: A One-Year Survey on Cases Presented to Two Veterinary Practices

Epidemiology and classification for canine and feline mammary gland tumors: a histopathological survey of 437 mammary gland tumor biopsies performed in a secondary care hospital in Chiang Mai, Thailand from 2012 to 2019

Background

Metastatic disease resulting from mammary gland tumors (MGTs) is a known cause of death among dogs and cats. Keys to successful prevention and management strategies involve the accurate recording of diagnostic data.

Methods

This retrospective study reviewed the epidemiology and classification of canine mammary gland tumors (CMTs) and feline mammary gland tumors (FMTs), as well as the factors including sex, age, and breed related to the occurrence of these tumors. Accordingly, 1,736 tumor biopsy cases were reported from 2012 to 2019 at Chiang Mai University Small Animal Hospital, Thailand, with 1,639 canine tumor biopsy cases and 97 feline tumor biopsy cases.

Results

The proportion of CMTs was reported at 24.5% (401/1,639) for all canine tumor biopsy cases. Benign and malignant tumors were reported at 14.5% (58/401) and 85.5% (343/401) for all CMT cases, respectively. The mean age of dogs affected by benign CMTs was 9.0 ± 3.0 years, which was significantly lower than for malignant CMTs at 9.9 ± 2.8 years (P = 0.0239). According to histopathological classification, benign mixed tumors and simple carcinoma types were highest among benign and malignant CMT cases, respectively. Moreover, female dogs were at significantly higher risk of developing mammary gland tumors (OR = 45.8, 95% CI [3.9-86.0], P < 0.0001) than male dogs, as well as older dogs (>8 years) (OR = 1.7, 95% CI [1.2-2.2], P = 0.0001) compared to young ones (≤8 years). The proportion of FMTs was 37.1% (36/97) for all feline tumor biopsy cases. Benign and malignant tumors for all FMTs were reported at 16.7% (6/36) and 83.3% (30/36), respectively. According to histopathological classifications, adenoma and simple carcinoma were present in the highest proportion among benign and malignant FMTs, respectively. Female cats were at a significantly higher risk of developing mammary gland tumors than male cats (OR = 25.7, 95% CI [3.9-272.8], P < 0.0001).

Conclusions and clinical importance

There was a high proportion of MGT cases compared with other tumor cases reported in a secondary care hospital in Chiang Mai, Thailand from 2012 to 2019, and malignant tumor biopsies have been more frequently observed than benign tumor biopsies in both CMT and FMT cases. The resulting data originating from this study can be an aid for veterinary oncologists in better educating clients and planning treatment and prevention strategies and it can be used as a basis for further experimental studies in the oncology section.

Risk factor analysis and clinicopathological characteristics of female dogs with mammary tumours from a single-center retrospective study in Poland

This is a comprehensive retrospective study to characterize female dogs with canine mammary tumors (CMTs) using a dataset retrieved from the archives of the Division of Animal Pathology, Institute of Veterinary Medicine in Warsaw, and to identify prognostic factors. Clinical and histopathological data of 1447 dogs with CMTs were included. Malignant tumours were found in 83.3% (n = 1206), benign tumours in 11.7% (n = 169), and non-neoplastic lesions in 5.0% (n = 72) of dogs. Dogs most often had grade II carcinomas (38.2%, 215/562) of a single histological subtype (88.5%, 1281/1447), mostly simple carcinoma (35.3%, 510/1447). Dogs with a median age of 10 years significantly often had larger (≥ 3 cm) and malignant CMTs, whereas intact females had smaller tumours (median size 2.0 cm). However, the threshold value for the age of the dog in the differentiation of malignant and non-neoplastic/benign masses could not be determined. Most females were hormonally active (76.4%, 372/487). Hormonally active dogs significantly more often had multiple tumours. Multiple tumours were significantly smaller (median 2.5 cm) than single ones. Among pedigree dogs, small-breed dogs were mostly recorded (43%, 428/1006). Twelve breeds had an increased risk of CMTs, regardless of tumour behaviour, compared with the theoretical distribution of pedigree dogs in Poland. Four breeds were often affected only by malignant and other four breeds only by non-neoplastic/benign CMT. Large-breed dogs were significantly younger and affected by larger CMT (median 4 cm) compared with small- and medium-breed dogs. Ninety dogs with a malignant CMT and complete records were included in the full analysis of CMT-specific survival (CMT-SS) with a median follow-up time of 20.0 months. We showed that the timing of ovariohysterectomy in relation to mastectomy was significantly associated with grade, CMT-SS, and CMT-related death. We indicated the low diagnostic accuracy of palpation of regional lymph nodes (RLN) in the prediction of their metastatic involvement. By multivariable analysis, dogs with neoplastic emboli, tumour ulceration, and simple or complex carcinoma had a significantly higher risk of local recurrence. Tumour size > 3 cm was as a strong independent predictor of lung metastases. Compared with dogs with an easily separated localized tumour, dogs with a multiple/diffuse malignant CMT pattern had a fivefold higher risk of death. The risk of death was significantly higher in the presence of neoplastic emboli (~ fivefold) and tumour ulceration (~ fourfold). Furthermore, the presence of neoplastic emboli and large tumour size were independent predictors of CMT-related death.

Mammary Glands of Women, Female Dogs and Female Rats: Similarities and Differences to Be Considered in Breast Cancer Research

Breast cancer is one of the most common and well-known types of cancer among women worldwide and is the most frequent neoplasm in intact female dogs. Female dogs are considered attractive models or studying spontaneous breast cancer, whereas female rats are currently the most widely used animal models for breast cancer research in the laboratory context. Both female dogs and female rats have contributed to the advancement of scientific knowledge in this field, and, in a "One Health" approach, they have allowed broad understanding of specific biopathological pathways, influence of environmental factors and screening/discovery of candidate therapies. This review aims to clearly showcase the similarities and differences among woman, female dog and female rat concerning to anatomical, physiological and histological features of the mammary gland and breast/mammary cancer epidemiology, in order to better portray breast tumorigenesis, and to ensure appropriate conclusions and extrapolation of results among species. We also discuss the major aspects that stand out in these species. The mammary glands of female dogs and women share structural similarities, especially with respect to the lactiferous ducts and lymphatic drainage. In contrast, female rats have only one lactiferous duct per nipple. A comprehensive comparison between humans and dogs is given a special focus, as these species share several aspects in terms of breast/mammary cancer epidemiology, such as age of onset, hormonal etiology, risk factors, and the clinical course of the disease. Holistically, it is clear that each species has advantages and limitations that researchers must consider during the development of experimental designs and data analysis.

Canine mammary gland disease in New Zealand: a review of samples from 797 dogs

AIMS

To evaluate the proportions of canine mammary gland lesions submitted to a New Zealand diagnostic laboratory, that were neoplastic vs. non-neoplastic lesions and, among neoplasms, malignant vs. benign, and to determine whether age, reproductive status or breed of dog, or size of the mammary mass were associated with the histological diagnosis.

METHODS

Canine mammary gland biopsies submitted between the start of 2012 and the end of 2016 were selected from the surgical biopsy database of IDEXX Laboratories, NZ. For each case, details on age, breed, and reproductive status of the patient were registered as reported by the submitting veterinarians, along with the size of the lesion and the histological diagnosis reported by the pathologists. χ² tests and independent sample t-tests were performed to evaluate associations.

RESULTS

Samples (n=895) were submitted from 797 dogs, of which 673 had mammary neoplasms while 124 had non-neoplastic lesions. Neoplasms composed of a single nodule were found in 591/673 (87.8%) dogs while 82/673 (12.2%) dogs had multiple nodules. Of the total 771 neoplasms, 432 (56.0%) were histologically malignant, while 339 (44.0%) were benign. Among malignancies, the most common histological sub-types were simple carcinoma (160/771; 20.8%), complex carcinoma (54/771; 7%), and ductal carcinoma (32/771; 4.2%), while benign mixed mammary tumour (128/771, 16.6%) and complex adenoma (105/771; 13.6%) were the most frequently reported benign mammary neoplasms. Age (p=0.09), reproductive status (p=0.79) and size of the mass (p=0.21) were not significantly different between neoplastic and non-neoplastic lesions. However, neoplastic mammary gland lesions were more frequent in purebred dogs (612/671; 91.2%) than crossbred dogs (61/126; 48.4%; p<0.001). Age (p=0.15) reproductive status (p=0.36) or breed (p=0.45) were not significantly different between malignant and benign neoplasms. There was a significant strong association between size and histological benign or malignant status of a neoplasm (φ=0.65, p<0.001).

CONCLUSIONS

Most canine mammary gland samples submitted for examination were neoplastic with slightly more malignant than benign lesions. Masses submitted from purebred dogs were more likely to be neoplastic while large neoplasms were more likely to be malignant.

CLINICAL RELEVANCE

The present findings provide a first description of distribution of mammary gland lesions in a relatively large number of dogs in New Zealand, representing a preliminary investigation of canine mammary gland diseases in this country.

A retrospective study and survival analysis on bitches with mammary tumours spayed at the same time of mastectomy

The aim of the present study was to retrospectively assess whether spaying at the same time of mastectomy increased disease-free survival (DFS) in bitches with mammary tumours and to investigate the utility of clinical data when designing a surgical plan that includes gonadectomy. Characteristics of 225 bitches carrying 489 tumours were retrieved. Of the116 bitches that underwent surgery, 52 bitches underwent mastectomy and ovariectomy, 46 bitches underwent mastectomy alone, whereas 18 bitches were already spayed. Analysis by Kaplan-Meier and in-between groups comparisons using Student's T, Chi-square, and one-way ANOVA tests were performed. DFS was longer for bitches that underwent ovariectomy and mastectomy compared to those that were left intact (p = .00064) or were already spayed (p = .0098). Spaying status affected tumour size (spayed: 2.75 cm ± 2.72; intact: 1.76 cm ± 2.04; p = .039), but not malignancy (p > .05). Differences in age were detected between animals with benign and malignant tumours (years: 9.1 ± 2.8 and 10 ± 2.3; p = .004), with multiple and single tumours (years: 10.18 ± 2.6 and 9.3 ± 2.8; p = .007), and between purebred and mixed breed bitches (years: 10.46 ±1.78 and 9.27 ±2.68; p = .005). Malignant tumours were larger than benign ones (2.17 cm±2.31 and 1.34 cm ±1.82; p = .005) and size increased according to the degree of malignancy. DFS was shorter for animals presenting tumours >2 cm in size (p < .006) and with tumours in the first pair of thoracic mammary glands (p = .00009). Gonadectomy should be suggested to owners of intact bitches carrying mammary tumours and age, size of the tumour, and location should be carefully considered when performing surgery.

Breast tumour size as a predictor of hemostatic system status and endothelial function in dogs

The high level of morbidity of dogs from mammary gland tumours and deficiencies in the pathogenesis give relevance to study of the disorders of the hemostatic system for predicting the neoplasia process. Our research concerned the determination of markers of the hemostatic system and endothelial function at different sizes (≤ 2, 5–7 and >10 cm) of benign (n = 28) and malignant (n = 27) breast tumours in dogs, taking into account their histological structure. The progression of the tumour process was accompanied by a 1.24–1.81 times increase in the fibrinogen content in the benign forms and 1.39–2.38 times in malignant against the background of progressive excess accumulation of soluble fibrin. The results of coagulation tests indicate that the increase in blood coagulation, which correlates with the magnitude of tumours, occurred mainly externally. In malignant neoplasms reliable, compared to clinically healthy dogs, reduction of total fibrinolytic activity occurred due to deficient inhibition of tissue plasminogen activator by 1.62–2.03 times. Increase in the size of benign neoplasms was accompanied by increased activity of the α1-inhibitor of proteinases, and in malignant – only in tumours of the size of 5–7 cm, against the background of its decrease in dogs with small and giant neoplasia. The progression of the disease was characterized by an increase in the content of α2-macroglobulin in benign lesions from 1.19–1.24 times, malignant – from 1.25–2.03 times. At the same time, there was a deepening of oxidative stress, as evidenced by the excess accumulation in the blood of malondialdehyde by 1.29–1.70 times in benign tumours, and 1.58–2.73 times in malignant. Regardless of the pathomorphologic form, the magnitude of the neoplasia foci is directly correlated with excess accumulation of nitric oxide and the level of hypoproteinemia, and vice versa – the content of ceruloplasmin. Further research should be undertaken to study the hemostatic status in certain nosological forms of breast tumours in dogs, which will improve the diagnosis and development of effective treatment protocols.