Papillary lesions of the canine mammary gland: description and casuistryABSTRACT
The purpose of the study was to identify the casuistry of papillary mammary neoplasms in female dogs, describe their epidemiological (age, breed) and morphological characteristics, and determine the survival of patients. Overall survival was estimated using Kaplan-Meier curves and comparisons between groups were performed using the Cox Mantel log-rank test (p < 0.05 were considered significant). A study was carried out between 2005 and 2020 at the Laboratory of Comparative Pathology of the Institute of Biological Sciences of the Federal University of Minas Gerais. The study identified 288 female dogs with 353 papillary neoplasms, 36.93% benign (papilloma, sclerosing papilloma, and papilloma with carcinomatous areas in situ) and 63.06% malignant (non-invasive papillary carcinoma, invasive papillary carcinoma, invasive papillary carcinomas with micropapillary areas and micropapillary areas in situ, and solid papillary carcinoma). Papilloma (53.1%) and invasive papillary carcinoma (46.64%) were the most frequent. Most papillary neoplasms were smaller than 3.0 cm in size and presented no metastases in lymph nodes and no distant metastases. However, the invasive papillary carcinomas’ average size was larger than the papillomas and non-invasive carcinomas. Papillary neoplasms are often associated with other types of mammary neoplasms; thus the survival of most female dogs is difficult to determine.
Keywords:
histopathology; carcinoma; malignant; female dog; arborescent
RESUMO
O objetivo do estudo foi identificar a casuística das neoplasias mamárias papilares em cadelas, descrever suas características epidemiológicas (idade, raça) e morfológicas, e determinar a sobrevida das pacientes. A sobrevida global foi estimada por meio de curvas de Kaplan-Meier e as comparações entre os grupos foram realizadas pelo teste log-rank de Cox Mantel (P<0,05 foram considerados significativos). O estudo foi realizado entre 2005 e 2020, no Laboratório de Patologia Comparada do Instituto de Ciências Biológicas da Universidade Federal de Minas Gerais. Foram identificadas 288 cadelas com 353 neoplasias papilares, sendo 36,93% benignas (papiloma, papiloma esclerosante e papiloma com áreas carcinomatosas in situ) e 63,06% malignas (carcinoma papilar não invasivo, carcinoma papilar invasivo, carcinoma papilar invasivo com áreas micropapilares e áreas micropapilares in situ e carcinoma papilar sólido). Papiloma (53,1%) e carcinoma papilar invasivo (46,64%) foram os mais frequentes. A grande maioria das neoplasias papilares tinha tamanho menor que 3,0cm e não apresentava metástases em linfonodos nem metástases a distância. Entretanto, os carcinomas papilares invasivos apresentaram aumento no tamanho do tumor em relação aos carcinomas benignos e não invasivos. As neoplasias papilares estão frequentemente associadas a outros tipos de neoplasias mamárias, portanto a sobrevivência da maioria das cadelas é difícil de ser determinada.
Palavras-chave:
carcinoma; maligno; cadela; arborecente
INTRODUCTION
Papillary mammary lesions are composed of a heterogeneous group of lesions characterized by intraductal formations of arborescent epithelial proliferation with fibrovascular stroma supporting epithelial proliferation (Schnitt and Collins, 2013; Wei, 2016; Gamba et al., 2017, Cassali et al., 2020). They comprise a group of benign and malignant lesions, in which the presence of a layer of myoepithelial cells within the projections that outlines the epithelium helps to differentiate between benign and malignant lesions (Hill and Yeh, 2005; Wei, 2016; Gamba et al., 2017). The human classification of papillary mammary lesions brings papilloma and papillary carcinomas, these being divided into intraductal or non-invasive, encapsulated, invasive and solid carcinomas (Koerner, 2010; Jorns, 2016; Wei, 2016). Mammary gland neoplasms are the most common type in female dogs. In a study with 1511 canine mammary neoplasms, 12% were diagnosed as benign and malignant papillary lesions (Nunes et al., 2018). In that species, papillary lesions comprise papillomas and carcinomas, which may be non-invasive papillary carcinoma and invasive papillary carcinoma (Gamba et al., 2017). However, no other study describing the characteristics and casuistry of papillary lesions of the canine mammary gland was found in the consulted literature. Therefore, the objective of the present article is to identify the casuistry of papillary mammary neoplasms in female dogs, with emphasis on the epidemiological and morphological characteristics, and to determine the survival of patients with mammary papillary lesions.
MATERIAL AND METHODS
A retrospective study of mammary neoplasms cases in female dogs was carried out by analyzing samples from 2005 to 2020, which were diagnosed at the Laboratory of Comparative Pathology (LPC) of the Institute of Biological Sciences of the Federal University of Minas Gerais (ICB - UFMG). Samples diagnosed as benign and malignant papillary neoplasia were selected, later revised, and classified according to the criteria adopted by the Consensus Regarding the Diagnosis, Prognosis and Treatment of Canine and Feline Mammary Tumors - 2019 (Cassali et al., 2020). Benign neoplasms were histologically classified as papilloma, sclerosing papilloma, and papilloma with carcinomatous areas in situ. The malignant neoplasms were classified as non-invasive papillary carcinoma (NIPC), invasive papillary carcinoma (IPC pure), which is further divided into IPC with micropapillary areas (IPC mi), and IPC with micropapillary areas in situ (IPC mi in situ), and solid papillary carcinoma (SPC). Lymph nodes were also evaluated for metastasis. Histological grading was performed according to the Nottingham System adapted for canine neoplasms (Elston and Ellis, 1991). The clinical tumor staging (TNM) of the patient was established using the criteria adopted by the World Health Organization (WHO) (Owen, 1980), which is based on tumor size (T), lymph node metastasis (N), and distant metastasis (M), the latter obtained through the medical record or information provided by the owner.
All breed, age, macroscopic (size and ulceration), and microscopic characteristics data were tabulated in Excel 2013, in which frequencies were calculated. The chi-square test was used to associate histological types and sizes. The specific survival was defined as the period in days between the surgical excision of the tumor and the death due to the tumor. The dogs were monitored by telephone with the owner, with an estimated minimum period of two years after surgical excision, and this was related to histological types. To calculate survival, female dogs that only had papillary-type neoplasms were considered; those with neoplasms with a worse prognosis were disregarded. For survival analysis, female dogs presenting only papillary mammary neoplasm were considered and was estimated using Kaplan-Meier curves. The analyses were estimated using Med Calc (MedCalc Software Ltd, Ostend, Belgium). Comparisons between groups were performed using the Cox Mantel log-rank test. Values of p < 0.05 were considered significant.
RESULTS
The study identified 288 female dogs with 353 papillary neoplasms, 36.93% (130/353) benign and 63.06% (223/353) malignant. Among benign tumors, papillomas represented 53.1% (69/130), followed by papilloma with carcinomatous areas in situ with 29.2% (38/130) and sclerosing papilloma with 17.7% (23/130). Malignant neoplasms were diagnosed as invasive papillary carcinoma (IPC) (104/46.64%), non-invasive PC (NI PC) (58/26.01%), solid PC (SPC) (31/13.91%), invasive PC with micropapillary areas (15/6.72%) (PC mi), invasive PC with micropapillary areas in situ (15/6.72%) (PC mi in situ). In general, female dogs with defined breed were more affected, representing 72.22%, with Poodle being the most common (74/208; 35.58%).
For the survival study, 43 female dogs with only papillary neoplasms were used. Of those, 19 (44.2%) were intact, 19 were spayed (44.2%) and 5 (11.6%) lacked information about their reproductive status. The use of contraceptives was identified in only 2 female dogs (4.7%), 32 (74.4%) had no history of contraceptive use and 9 lacked such information. Staging was performed in 28 female dogs, with a higher frequency in staging I with 13 female dogs (30.2%), II 2 with (4,7%), III with 4 (9,3%), followed by 9 (20.9%) female dogs in stage IV. In the evaluation of tumor size, 22 (52.4%) tumors it T1, 5 (11.9%) were T2, 12 (28.6%) T3, and 3 (7.1%) lacked information on their sizes. Histologic grade was reported in only 17/165 invasive malignant neoplasms, with grade II being the most common. No differences were seen in the specific survival of female dogs with different types of malignant papillary neoplasms. Also, no significant differences were found between types of papillary lesions when comparing size, grade, lymph node metastasis, adherence and ulceration, mitotic index, staging, and survival (Fig. 1). The clinical-pathological characteristics (age, lesion size, ulceration, lymph node metastasis, stating) found are subdivided by histological type and described in Table 1.
Survival curve (Kaplan-Meier) of female dogs with malignant papillary neoplasms of the mammary gland. NI CP: non-invasive papillary carcinoma; IPC mi in situ: Invasive papillary carcinoma with micropapillary areas in situ. IPC mi: Invasive papillary carcinoma with micropapillary areas; CPI: Invasive papillary carcinoma; SPC: Solid papillary carcinoma; Pap carc in situ: Papilloma with carcinomatous areas in situ.
Ductal papilloma is a benign neoplasm originating from the ductal epithelium in a papillary or arborescent format that projects into the lumen, and can present a single or multiple formation (Fig. 2A). The papillary formations, which arise from the fibrous connective tissue that forms the duct wall, are lined by epithelial cells arranged in a single layer, supported by a layer of myoepithelium (Fig.2B, C). The mitotic index is low. Among the cases providing information on animal age (65/69), the mean age was 117.9 months (9.8 years). Other clinical data, such as the use of contraceptives, observation of the estrous cycle - regular or irregular - and pseudocyesis were not informed by the guardians in most cases. The right and left mammary chains were affected in the same proportion (32/46.38%) and only 3 cases (4.35%) presented bilateral involvement.
Papillomas were frequently present in female dogs as other neoplastic types in other mammary glands (55/69, 79.71%). Sclerosing papilloma is characterized by collagenization of the papilloma’s fibrovascular stroma, which can cause compression of the epithelial cells lining the papilla, making it difficult to identify the basement membrane and the myoepithelial layer (Fig. 2D, E). The majority of these tumors were T1 and the inguinal mammary gland was the most frequently affected (8/25). The right chain was the most affected (13/56, 52%) and 21 from 23 cases of this type of papilloma (91.3%) were associated with other mammary neoplasms in other glands. Papilloma with carcinoma areas in situ (Pap carc in situ) shows histological aspects of the papilloma with areas of carcinomatous transformation with no basement membrane invasion (Fig. 2F). These areas are characterized by multiple layers of epithelial cells, more eosinophilic cytoplasm, nucleus with anisokaryosis and evident nucleolus. Most of the lesions did not show ulceration and/or adherence. Regarding tumor size, the values for 34 neoplasms were obtained, most of which were classified as T1 (23, 60.52%). Among the 30 lymph nodes that were evaluated, 28 (73.68%) did not present metastasis. The caudal abdominal mammary gland was the most affected (12/42), while left and right chains were equally affected (18/38).
Histological aspects of benign papillary lesions of the mammary gland of female dogs. A. Papilloma. Arboriform or papillary projections into the duct, H&E, Scale Bar = 50 µm. B. Papillary formations arising from the fibrous connective tissue of the ductal wall, delineated by organized epithelial cells, H&E, Scale Bar = 100 µm. C. Abundant collagenous stroma of the papilla (*), and the presence of myoepithelial cells (arrowhead) between the fibrous tissue and the epithelium, H&E, Scale Bar = 50 µm. D. Sclerosing papilloma. Nodular proliferation with a thick capsule of collagenous tissue (*) compressing the ducts (arrow), H&E, Scale Bar = 100 µm. E. Compression of ducts and epithelial cells by the large amount of collagen (arrow), H&E, Scale Bar = 50 µm. F. Papilloma with carcinomatous area in situ. A papilla showing area with a layer of well-differentiated and organized epithelial cells supported by a fibrous stroma (arrow), and the epithelium in the contralateral portion of the papilla is proliferated with multiple layers of epithelial cells, hyperchromatic nucleus - carcinomatous area (head of the papilla). arrow), H&E, Scale Bar = 20µm.
Papillary carcinomas can be defined as numerous intraluminal projections with arborescent arrangement covered by multiple layers of epithelial neoplastic cells supported by delicate fibrovascular stroma.
Non-invasive papillary carcinoma (NI PC) is defined as a well-delimited lesion, surrounded by a capsule of fibrous tissue, restricted to the galactophore duct (Fig. 3A). The papillae are covered by multiple layers of epithelial cells supported by a thin fibrovascular septum (Figure 3B). Such a lesion is usually presented as a single lesion. None was ulcerated and most also did not present adherence. Of those 57 neoplasms, 37 (63.79%) were classified as T1. Only two female dogs presented metastasis to the regional lymph node. Most lesions occurred in the inguinal mammary gland.
Invasive papillary carcinoma (IPC) is similar to NI PC but presents disruption of the basement membrane of the duct wall with subsequent invasion of epithelial cells from the adjacent stroma surrounding the neoplasm (Fig. 3C, D). Most of the lesions (more than 90%) did not show ulceration and/or macroscopic adherence. Among the 96 cases measured, 57 (54.81%) were classified as T1. Most female dogs with lymph node status inflammation did not show metastasis (50, 49.02%). The inguinal mammary gland was the most affected, followed by the caudal and cranial abdominal mammary glands.
Invasive papillary carcinoma with micropapillary areas in situ (IPC mi in situ) has the characteristics of IPC, but with formations of micropapillae (without fibrous connective tissue stroma) that project into the ductal lumen and do not go beyond the basement membrane of the papilla. In this histological type, often did not present ulceration and adherence; 4 (26.67%) were T1, and 7 (46.67%) were T3. The lymph node evaluation had present in 12 female dogs, being that 8 (53.33%) of them showed no evidence of metastasis and distant metastasis was present in only 1 female dog out of the 7 reported cases. This histological type was more frequent in the caudal abdominal mammary gland.
Invasive papillary carcinoma with micropapillary areas (IPC mi) also presents the same characteristics described for invasive carcinoma, but the areas of micropapilla formations present an important and frequent characteristic in the neoplasm, which is the ability to invade the adjacent capsular stroma. The clinico-pathological characteristics were similar to IPC mi in situ.
Solid papillary carcinoma (SPC) is characterized by exacerbated proliferation of epithelial cells with solid mass formation by the convergence of papillary projections, with a thin and delicate fibrous septum between the epithelial portion and with no presence of myoepithelial cells. The differential diagnosis of solid-type carcinomas must be made by observing the fibrovascular stroma, which can be extremely thin. (Fig. 3E, F). The inguinal mammary gland was the most affected (10/31; 32.26%) and both mammary chains were equally affected (12/31; 38.71%). Most of these lesions were smaller than 3.0 cm, fitting in T1, 19 (61.3%).
DISCUSSION
Papillary lesions of the mammary gland are considered a challenge for human medicine, mainly regarding the variety and differentiation between benign and malignant lesions (Rakha and Ellis, 2018; Kulka et al., 2022). In veterinary medicine, papillomas are among the most common benign neoplasms in female dogs, second only to benign mixed tumors. Invasive and non-invasive papillary carcinomas also represent an important percentage of female dogs; however, they are not the most common (Nunes et al., 2018; Silva et al., 2019). Similar to women, female dogs also have a variety of neoplasms with papillary arrangements in the mammary gland, but the histological differentiation is often difficult, not standardized, and little is known about the growth behavior of each type. In the present study, female dogs frequently presented other histological types of mammary tumors in addition to papillary neoplasms. It is also common to see more than one lesion of the papillary type. A total of 288 female dogs and 353 papillary lesions were counted and only 43 female dogs had only papillary lesions (benign and/or malignant) or had papillary carcinomas as the neoplasm of worst prognosis. That fact made it difficult to establish survival criteria in those female dogs. Most female dogs with papilloma also have another malignant mammary neoplastic type, in agreement with findings that show it is common for female dogs to have multicentric mammary tumors (Toríbio et al., 2012; Silva et al., 2019).
Histological aspects of malignant papillary lesions of the mammary gland of female dogs. A. Non-invasive papillary carcinoma, nodular neoformation, well delimited with multiple papillary projections into the ductal lumen, with high cellularity, H&E, Scale Bar = 200 µm. B. Close-up image of a papilla with thin septa of fibrous connective tissue lined by multiple layers of columnar epithelial cells, H&E, Scale Bar = 200 µm. C. Invasive papillary carcinoma, intraductal papillary proliferations, but also note papillary formations infiltrating adjacent tissue H&E, Scale Bar = 200 µm. D. Invasive papillary neoplastic formations (arrow), H&E, Scale Bar = 100 µm. E. Solid papillary carcinoma, marked proliferation of papillary epithelial cells supported by thin septa of fibrous tissue (arrow) giving a solid appearance, H&E, Scale Bar = 100 µm. F. Fibrous tissue in blue (arrow) and epithelial proliferation (*), Masson's Trichrome, Scale Bar = 50 µm.
Regarding the age of the animals, no statistical difference was observed between benign and malignant papillary histological types, as reported by several studies that encompass different histological types. Older female dogs are commonly shown to have a greater chance of developing malignant neoplasms than younger female dogs (Nunes et al., 2018). In women, papillomas are also more frequent under 55 years of age and papillary carcinomas are more frequent in older women (Schnitt and Collins, 2013; Rakha and Ellis, 2018).
Macroscopic ulcerations and adhesions were rare in all papillary histological types, which can be explained by the slow growth in those histological types, even in malignant cases. Most neoplasms were small, with T1 being correlated with slow growth and consequently inducing less tumor necrosis. Invasive papillary carcinomas presented approximately 2cm more than benign ones, although that was not statistically significant. In addition, it was possible to observe that neoplasms presenting micropapillary are larger. In women, most papillomas are less than 1 cm (Schnitt and Collins, 2013).
Evaluation of metastasis and staging information was not possible in all cases due to the lack of information in the medical records and from the guardian, but most female dogs with papillary carcinomas did not present lymph node or distant metastasis. Another difficulty in evaluating those variables was that most of the animals had other types of mammary malignancies, such as carcinoma in mixed tumor, solid pattern carcinomas, pure micropapillary carcinoma, or associated with other types.
The differentiation between benign and malignant papillary lesions is often challenging. The more delicate and less fibrotic stroma in malignant lesions compared to benign lesions can help in that process (Rakha and Ellis, 2018; Wei, 2016; Kulka et al., 2022). In the diagnoses performed, that feature was used to differentiate types of papilloma from well-differentiated non-invasive carcinoma. In addition, the presence of myoepithelial cells and the definition of a basement membrane at the epithelium/stroma interface is evident in benign lesions (Rakha and Ellis, 2018) but in some cases, such observation is more difficult, especially in papillomas with carcinomatous areas. In cases of sclerosing papilloma, the abundant fibrous stroma can cause compression of the duct cells, creating an infiltrating appearance, and the cells can have reactive characteristics, which can mimic an invasive carcinoma (Schnitt and Collins, 2013; Jorns, 2016). In this case, the identification of myoepithelial cells between the epithelium and the stroma is what aids in the diagnosis. Some authors suggest performing immunohistochemistry for myoepithelial cells with p63 (Wei, 2016, Kulka et al., 2022). The presence of a well-delimited intraductal lesion, consisting of fibrovascular stroma covered by a layer of benign myoepithelial cells and externally by epithelial cells, helps in the diagnosis of papillomas. When there is proliferation of small solid or cribriform foci of epithelial cells exhibiting a monomorphic appearance, the presence of atypical areas can be considered (Schnitt and Collins, 2013; Jorns, 2016). Those characteristics allow the identification of papillomas and papillomas with atypical and carcinomatous areas in situ.
Papillary carcinoma in women exhibits an encapsulated intraductal growth form that resembles our description of non-invasive papillary carcinoma, with papillary proliferation surrounded by a fibrous capsule. In women and female dogs, myoepithelial cells are not present in the papillae of this neoplastic type, however, immunohistochemistry for p63 is the best way to confirm this absence (Schnitt and Collins, 2013; Gamba et al., 2017).
The solid papillary carcinoma was recently described in veterinary medicine (Nakagaki et al., 2022) and its histological organization pattern is very important for the diagnosis. In human medicine, such histological type most often presents growth in situ into ducts and rarely presents invasive behavior (Kulka et al., 2022). Few cases are still reported in veterinary medicine, but worse behavior than that described in women is suggested (Nakagaki et al., 2022). Therefore, pathologists should be aware of that diagnosis, so that the true biological behavior of the lesions can be better understood.
CONCLUSION
There is a variety of canine mammary gland papillary neoplasms and little has been defined about their behavior compared to other histological types and treatment. They are often present in female dogs with other types of mammary neoplasms, which makes the prognostic evaluation difficult. Although the present study did not find statistical correlations between malignant and benign types and difference in the survival of patients with those lesions, other studies are needed to better define prognostic factors and treatment of such lesions in female dogs.
ACKNOWLEDGMENTS
This work was financially supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundaçāo de Amparo á Pesquisa de Minas Gerais -FAPEMIG [Rede Mineira de Pesquisa Translacional em Imunobiológicos e Biofármacos no Câncer (REMITRIBIC, RED-00031-21)] and Coordenaçāo de Aperfeiçoamento Pessoal de Nível Superior (CAPES), Brazil.
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Publication Dates
-
Publication in this collection
27 Jan 2025 -
Date of issue
Jan-Feb 2025
History
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Received
05 Feb 2024 -
Accepted
18 June 2024
