Publishing Authors : Elena Atanaskova Petrov, Ksenija Ilievska, Plamen Trojacanec, Irena Celeska, Goran Nikolovski, Ivica Gjurovski, Toni Dovenski.

Date Published : 12/05/14


The mammary gland is a compound
tubuloalveolar gland, divided into lobules by
interlobular connective tissue. The mammary gland
consists of parenchyma (alveoli), stroma (connective
tissue), ducts, vessels and nerves. Bitches usually
have fi ve pairs of glands. The cranial two pairs are
referred to as cranial and caudal thoracic mammary
Elena Atanaskova Petrov1
, Ksenija Ilievska2
, Plamen Trojacanec2
, Irena Celeska3
Goran Nikolovski1
, Ivica Gjurovski4
, Toni Dovenski5
Department of Small Animal Internal Medicine and Horses,
Department of veterinary surgery, 3
Department of Pathophysiology
Department of Pathology and Forensic Medicine, 5
Department of Reproduction
“Ss. Cyril and Methodius” University in Skopje, Faculty of Veterinary Medicine Skopje
Lazar Pop- Trajkov 5-7, 1000 Skopje, R. Macedonia
Received 26 February 2014; Received in revised form 2 April 2014; Accepted 12 May 2014
Mammary tumours are the second most frequent neoplasia in dogs, mainly affecting older female patients. Approximately
50% of the mammary tumours are malignant with high percentage of mortality, if not treated in time. The aim of this study
was to analyze the data of canine patients with mammary tumours, to evaluate the type of tumours, as well as the relationship
between tumour incidence and dogs’ age, reproductive cycle and sterilization. The survey was used to retrieve the information
in the period of two years from the patient data base of the University Veterinary Hospital at the Faculty of veterinary
medicine in Skopje. Patients included in this survey were subjected to routine clinical investigation and additional laboratory
tests (cytological examination, x-rays imaging, CBC and biochemical profile, histopathology of the tumor samples). Aged
female patients (12 – 13 years) are the most susceptible category for development of mammary tumours. The reproductive
history showed that five of the patients with malignant mammary tumours have never whelped and were not treated with any
exogenous hormones. Malignant tumours (adenocarcinoma) were diagnosed in 90% of the patients. Three patients died due to
lung metastasis. Late diagnosis is one of the major problems that results in lethal outcome due to lung metastases. Since ovarian
steroids play an important role in the aetiology, the most effective prevention of mammary tumours is elective ovariectomy of
the bitch at an early age.
Key words: mammary tumours, bitches, cytology, histopathology
Corresponding author: Prof. Toni Dovenski, PhD
E-mail address:
Present address: Faculty of Veterinary Medicine-Skopje;
Department of Reproduction;
Lazar Pop Trajkov 5-7, Skopje, Macedonia;
Phone: ++38923240767
Copyright: © 2014 Atanaskova Petrov E. This is an open-access article
published under the terms of the Creative Commons Attribution License
which permits unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are credited.
Competing Interests: The authors have declared that no competing
interests exist.
Available Online First: 16 May 2014
glands, the middle two pairs are referred to as cranial
and caudal abdominal mammary glands, and the
caudal pair is referred to as the inguinal mammary
glands. After the skin, mammary gland is the second
most common site for tumour development in dogs.
Mammary tumours are the most frequent neoplasms
in bitches. They represent approximately 42% of
all tumours and 82% of those arising on the female
reproductive organs (1, 2).
Benign mammary tumours appear earlier in life
than malignant ones, a
Atanaskova Petrov E. et al.
breed dogs have been reported to have an increased
incidence of mammary neoplasia (5). Mostly affected
parts are caudal abdominal and inguinal mammary
glands. Multiple tumours have been seen in 50% to
almost 70% of dogs with mammary tumors (2, 4, 6).
In case of multiple tumours, different tumour types
may be present within one animal. According to
some authors 50% of the tumours are malignant, the
majority of malignant mammary tumors in dogs are
carcinomas and <5% are sarcomas (7).
Group of authors have concluded that malignant
tumours are significantly larger than benign
tumours. Also, evidence of histological progression
towards malignancy has been seen with increasing
tumour size. These findings suggest that mammary
tumours can progress from benign to malignant (4).
The action of ovarian hormones (estrogens and
progesterone) on mammary gland tissue during
different stages of development is a risk factor
associated with the development of mammary
tumors. A preventive effect of spaying on the
development of mammary tumors has been reported.
Early ovariectomy in dogs and cats has a protective
effect against both benign and malignant mammary
tumours. (8) The risk of developing a mammary
tumour increases as the number of estrous cycles
increases. The risk of developing mammary gland
tumours is 0.05% if the bitch is spayed prior to the
first estrous cycle. An increased incidence of tumour
development also has been observed in dogs that
received injectable progestins for the prevention of
estrus (9).
It has been reported that most of the dogs are
clinically healthy when they are initially presented
for clinical examination (2). If metastases are
present, dogs may show nonspecific symptoms such
as fatigue, lethargy, weight loss, dyspnoea, cough,
lymphoedema or lameness. The extent and location
of the metastases determines the occurrence and
severity of the clinical signs (2, 6). Initial assessment
of canine mammary tumour is based on basic patient
data (age, age at ovariohysterectomy, history of
clinical signs duration, reproductive cycles, lactation,
synthetic progestagens therapy), general condition
and physical examination (2, 6, 7). Surgery remains
the basic treatment for dogs with most common type
of mammary gland tumours (benign mixed tumor,
adenoma, and adenocarcinoma). The adjuvant
therapies (radiation therapy and chemotherapy) are
used for inoperable tumours and in inflammatory
carcinoma. The survival time after the mastectomy
and the possibility of metastases have been reported
as main clinical complications (10).
The aim of this retrospective study was to present
clinical cases of canine mammary tumours recorded
at the University Veterinary Hospital in Skopje
in the period of two years, to evaluate the type of
mammary tumours in the patients; to analyze the
relationship between tumor incidence and the age of
the patients, heat cycles and sterilization, as well as
the survival period after surgery.
During a period of two years, canine patients
have been submitted to medical and surgical
treatment after diagnosing various types of tumours
at the University Veterinary Hospital at the Faculty
of veterinary medicine in Skopje. Ten patients were
diagnosed with mammary tumours.
Breed, age, location of the affected mammary
glands, tumour size (maximal diameter of the
tumour), period (in days) between the fi rst detection
by the owners and the time the patient was brought
for treatment, reproductive history (spaying status,
age at spaying, whelping and history of false
pregnancy), application of exogenous hormones
and type of surgery (radical mastectomy) were
obtained from review of medical records. Patients
were thoroughly examined (assessment of general
condition, temperature, pulse, respiration, palpation
of the lymph nodes, CBC and serum biochemical
profi le (ALT, AST, AP, creatinine, urea).
After the initial examination and the lab results,
fi ne needle aspiration (FNA) was performed using
a 22-G needle on each mammary mass, in order
to make the initial determination of the mass. At
least 4 samples from different areas were obtained
from each mass and at least 1 slide was prepared in
a standard procedure for each aspirate. The slides
were air-dried and stained with Diff Quick staining
(Merck, Darmstrad, Germany) and evaluated under
a light microscope (Nikon; 40 X magnifi cation).
In addition, chest radiographs were taken before
the planned surgical treatment. Surgical removal
of the masses was treatment of choice (complete
mastectomy with or without ovariohisterectomy).
The owners were offered an adjuvant therapy
(chemotherapy) however, none of them accepted the
procedure due to the side effects of chemotherapy
as well as the high price of chemotherapeutic
medications. Histopathological examination of the
excised tumours was performed at the Department of
Pathology at the Faculty of Veterinary Medicine in
Skopje. Following surgical excision, tissue samples
Canine mammary tumors – clinical survey
were fi xed in 10% formaldehyde, embedded in
paraffi n, cut into 4 μm sections, and stained with
hematoxylin and eosin. Histological evaluation was
performed according to the WHO classifi cation
scheme for canine mammary tumours. Canine
mammary tumours are histologically classifi ed into
four categories: malignant tumours, benign tumours,
unclassifi ed tumours, and mammary hyperplasia/
dysplasia (11).
The majority of the patients (6 out of 10) with
diagnosed mammary tumours were at the age of
12 – 13 years. The youngest patient with mammary
tumour was 6 years old. From a reproductive point of
view, five of the patients with malignant mammary
tumours have never been whelped and never treated
with any exogenous hormones; one was treated
with synthetic progesterone before every cycle, two
were with unknown history. The patients were of
different breed (Doberman Pincher, French Poodle,
Miniature Schnauzer, Dalmatian, Cocker Spaniel,
Irish Setter, Belgian Sheepdog and two of mixed
Multiple nodular appearance of the tumour was
found in 6 patients (Figure 1, 2), while 4 patients
had solitary tumour mass.
In nine patients, with malignant tumors (90%),
one was diagnosed as adenoma. Cytological
examination of the samples (n=5) revealed lobular
adenocarcinoma (Figure 3). Pathohistological
examination of the mammary tumor samples (n=5)
revealed tubuloalveolar adenocarcinoma (n=4)
and ductal adenocarcinoma (n=1). Chest x-ray
imaging was recommended for all patients with
adenocarcinomas, but only 5 made it. In 3 out of
5 of the patients with diagnosed adenocarcinoma
lung metastases were noted by the X-ray imaging.
Dimensions of the malignant mammary tumours
were between 5 and 10 cm.
The only treatment was surgical removal of
the tumours (simple or radical mastectomy). The
owners of seven patients agreed to additional
ovariohysterectomy. Radical mastectomy was
performed in patients that had multiple mammary
tumours. Three patients died between 20 days and
2 months after the surgery. They were presented
in the Hospital with sings of dyspnea due to lung
metastases, anorexia, vomiting, decreased body
temperature and lethargy. The rest of the treated
patients (n= 7) were monitored on a monthly basis.
Six months after the treatment, these patients
remained in good body condition, without any signs
of health disorders. They are recommended and visit
the hospital on regular check-ups every 6 months.
Figure 1. Mammary tumour of the cranial and caudal
abdominal mammary gland- left side (6 year old
Doberman Pinscher)
Figure 2. Mammary tumour on the cranial thoracal mammary gland (right) with metastases on the ingvinal mammary
gland (9 year old Belgian Sheepdog)
Atanaskova Petrov E. et al.
In this study, older dogs (12-13 years), were
predominantly affected by mammary tumours.
Similarly, Murphy (9) reported predominance of
mammary tumours in bitches at the age of 10 – 11
year, and seldom before the age of 2 years (9).
Other research group reported the highest incidence
of mammary tumours in patients between the age
of 6 and 10 years (up to 63%), 32% of incidence in
patients older than 10 years and only 5% in patients
younger than 5 years. (12)
Ovarian steroids stimulate growth of normal
mammary tissue under physiological conditions in
bitches. Their proliferative effect on the epithelium
may create conditions for neoplastic proliferation (13,
14). This occurs during every cycle and renders the
bitch more susceptible to carcinogenesis. Oestrogens
promote ductal growth, whereas progestins are
able to induce a lobuloalveolar development of
the mammary glands with hyperplasia of secretory
and myoepithelial cells (5). Bitches that are spayed
before the fi rst oestrus have a 0.5% risk; animals
spayed before the second oestrus have an 8% risk,
and those spayed after the second oestrus and before
two and a half years of age have a 26% risk of
developing mammary tumours compared with the
intact ones (15). It had been reported that exogenous
administration of progesterone derivates, which are
used to prevent oestrus in dogs, may increase the
incidence of canine mammary tumours. Synthetic
progestins (such as medroxyprogesterone acetate)
induce the same effect on the mammary gland as
endogenous progesterone. One clinical study on
dogs treated with medroxyprogesterone acetate
for oestrus prevention reported a greater risk of
Figure 3. FNA sample from canine mammary tumour (Diff Quick, 100x)
developing mammary tumours, the majority being
malignant. (16)
In our study as well as in other studies (17, 18)
dogs were admitted in the clinic for examination
and treatment, roughly a year after the fi rst detection
of the mass. In our study 6 patients (66%) were
with multiple mammary tumours. Similarly, other
authors reported 50% to almost 70% of multiple
tumours in dogs with diagnosed mammary tumours
(2, 4, 6, 19). The majority of malignant tumours
of the mammary gland in dogs are carcinomas (7),
in our study carcinoma was diagnosed in 89% of
the patients. Other study has shown that dogs with
malignant tumours were significantly older than
dogs with benign tumours, and malignant tumors
were significantly larger than benign tumours (4).
Five mammary tumours were examined at the
Department of histopathology and were diagnosed
as carcinomas (adenocarcinoma), which is the most
common type of canine mammary tumour. (20)
The main treatment of canine mammary
tumours is surgery, except for inoperable highly
metastatic disease (6, 7). Surgical excision allows
histopathological diagnosis and can be curative
if the margins are clean and if the cancer has not
spread (21). Dogs with benign tumours and
approximately 50% of dogs with malignant
mammary tumours will successfully recover if
treated on time and depending on size of the
tumour (22). The other 50% of the patients with
malignant mammary tumours already has metastases
at the time of surgery, which will eventually lead to
death of the patient (6). The incidence of malignant
mammary tumours in our study was 43.5%, similar
to Moe (2001) who reported an incidence of 53.3%
(23). Certain authors advice more radical surgery
Canine mammary tumors – clinical survey
(24) because their study showed new tumour
development in 58% of the patients in the ipsilateral
mammary tissue after local removal of a solitary
canine mammary tumour. In our study, radical
mastectomy was done in 6 (66%) patients that
had multiple mammary tumours. Literature shows
contradicting results regarding the benefit of
ovariectomy at the time of the excision of the
mammary tumours (25). Only 2 patients in our
study, with large tumor masses, were submitted to
ovariohysterectomy and until present no signs of
distant metastasis were detected.
Mammary tumours are common tumors and
often present in older intact female patients. Late
diagnosis is one of the major problems that results
in lethal outcome due to lung metastases. Dogs with
canine mammary tumours need a full diagnostic
work-up, and every mammary tumour should
be excised and submitted for histopathological
examination. Since the ovarian steroids play an
important role in the aetiology, the most effective
prevention of mammary tumours is elective
ovariectomy of the bitch at an early age.
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