Radiol Oncol 2018; 52(1): 98-104. doi: 10.1515/raon-2017-0057
98
research article
Electrochemotherapy with bleomycin of 
different types of cutaneous tumours in a 
ferret (Mustela putorius furo)
Jozko Racnik1, Tanja Svara2, Marko Zadravec1, Mitja Gombac2, Maja Cemazar3,  
Gregor Sersa3, Natasa Tozon4
1  Clinic for Birds, Small Mammals and Reptiles, Institute of Poultry, Birds, Small Mammals and Reptiles, Veterinary Faculty, 
University of Ljubljana, Ljubljana, Slovenia
2 Institute of Pathology, Wild Animals, Fish and Bees, Veterinary Faculty, University of Ljubljana, Ljubljana, Slovenia
3 Institute of Oncology Ljubljana, Ljubljana, Slovenia
4 Small Animal Clinic, Veterinary Faculty, University of Ljubljana, Ljubljana, Slovenia 
Radiol Oncol 2018; 52(1): 98-104.
Received 3 October 2017 
Accepted 5 November 2017
Correspondence to: Jozko Racnik, Ph.D., Clinic for Birds, Small Mammals and Reptiles, Institute of Poultry, Birds, Small Mammals and 
Reptiles, Veterinary Faculty, University of Ljubljana, Cesta v Mestni log 47, SI-1000 Ljubljana, Slovenia; E-mail: josko.racnik@vf.uni-lj.si
Disclosure: no potential conflicts of interest were disclosed. 
Background. Mast cell tumour, sebaceous gland adenoma, and less common squamous papilloma are skin tu-
mours in ferrets (Mustela putorius furo), and early excisional surgery is usually the treatment of choice. The aim of 
our study was to investigate the effectiveness of electrochemotherapy (ECT), a new, minimally invasive non-surgical 
method, as first treatment option of different types of ferret skin tumours located on surgically difficult sites. 
Materials and methods. A 5-year-old castrated male ferret with two cutaneous masses, presenting 4 months apart 
and a 7-year-old spayed female ferret with two cutaneous masses, that appeared simultaneously on two locations 
are presented. In the first patient, both masses were diagnosed as mast cell tumours, and in the second patient, 
squamous papilloma and sebaceous adenoma were diagnosed. One session of ECT with bleomycin injected intra-
tumourally was applied in all tumours.
Results. Complete response (CR) of all tumours was obtained, without recurrence during observation period of 15 
months after ECT for first tumour and 11 months after ECT of the tumour located on the right hock in first patient, and 
8 months after treatment for the second patient. 
Conclusions. In present study, ECT with bleomycin proved to be safe and effective against different cutaneous 
tumours in ferrets. Due of good results, low cost and relatively easy procedure, ECT could be the treatment of choice 
instead of surgery for the selected skin tumours in ferrets.
Key words: electrochemotherapy; bleomycin; cutaneous tumours, ferret
Introduction
Tumours are common health problem in domestic 
pet ferrets (Mustela putorius furo), most commonly 
affected are endocrine, integumentary and lym-
phatic system.1 Mast cell tumours (MCTs) and se-
baceous tumours (sebaceous epitelioma, sebaceous 
adenoma) are most prevalent tumours of the skin.2 
Most frequently, MCTs appear on the extremi-
ties, following the trunk and head or neck. They 
are usually small (1‒4 mm in diameter), round to 
plaque-like nodules with surface crusting.3 In some 
cases, animals develop local pruritus, and overlying 
skin may be ulcerated due to self-trauma.1 In ferrets, 
MCTs are considered clinically benign and they do 
not spread locally or metastasize.1,3 However, there 
are some suggestions about visceral involvement 
and malignant behaviour of this tumours.4
Sebaceous adenomas are benign tumours, which 
involve only skin and may occur anywhere on the 
Radiol Oncol 2018; 52(1): 98-104.
Racnik J et al. / Electrochemotherapy of tumours in ferrets 99
body. They are firm, warty and often multinodu-
lar, sometimes looking very similar to MCTs. They 
can be ulcerated, irritated and traumatised with lo-
cal inflammation.2,4 
Squamous papilloma is very rare skin tumour of 
ferrets with only one case noted in a study of 1,525 
ferret neoplasia’s collected in years 1990 to 2000.5 
Although there is some evidence that some squa-
mous cell carcinomas (SCC) of the skin in ferrets 
can be associated with papillomavirus6, possible 
viral aetiology of cutaneous squamous papilloma 
in ferrets was yet not investigated. Moreover, re-
cent publications suggested that, squamous papil-
loma of skin and conjunctiva in dogs are not con-
nected with papillomaviruses.7 
Fine needle aspiration (FNA), incisional or ex-
cisional biopsy are recommended to confirm the 
diagnosis of any cutaneous tumour.2 Early exci-
sional surgery is the treatment of choice, and wide 
surgical margins are always advisable.2,5 However, 
some tumours are large with invading surround-
ing tissue on unsuitable sites, which makes the 
closure of defect after surgery, and consequently 
preservation of function, difficult. ECT is a new 
anti-neoplastic therapy in veterinary medicine that 
combines administration of a chemotherapeutic 
agent, cisplatin or bleomycin, with electric pulses 
to the tumour.8 
The aim of our study was to investigate the ef-
fectiveness of electrochemotherapy (ECT), as a 
new, minimally invasive non-surgical method, for 
treatment of different types of ferret skin tumours 
located on surgically difficult sites. 
Materials and methods
Patients
First patient was a 5-year-old castrated male ferret 
with two cutaneous masses presented 4 months 
apart. First mass (0.8 cm x 0.8 cm x 0.5 cm) was lo-
cated on the laterodorsal tail base (tumour 1), while 
the second one (1.2 cm x 1.0 cm 0.7 cm) was found 
on the lateral side of the right hock (tumour 2). The 
ferret had no major health issues since the initial 
presentation, and masses apparently did not pro-
duce any health problems or discomfort. Regular 
health checks and vaccinations were carried out 
every year.  
Second patient was a 7-year-old spayed female 
ferret with two cutaneous masses that appeared 
simultaneously on two locations. First mass (0.7 
cm x 0.7 cm x 0.5 cm) was located on the lateral 
side of the left hock (tumour 3) (Figure 1), while 
the location of the second mass (0.4 cm x 0.4 cm 
x 0.2 cm) was dorsolateral on the left chest region 
(tumour 4). Before the initial presentation, the fer-
ret had a history of insulinoma managed with diet, 
corticosteroids and regular glucose measurements. 
On physical examination, both patients were alert, 
bright and responsive with body masses of 1700 g 
and 430 g respectively. Incisional biopsies of tu-
mours 1, 3 and 4, and FNA of tumour 2 were ob-
tained under general gaseous anaesthesia, and his-
topathology and cytology were done. Briefly, sam-
ples for histopathology were fixed in 10% buffered 
formaline and routinely embedded in paraffin. 
Four-µm-thick sections were stained with hema-
toxylin and eosin and examined microscopically. 
Cytological smears were stained with Hemacolor 
(Merck®, Darmstadt, Germany).
Histopathological examination of the tumour 1 
presented as nonencapsulated, slightly infiltrative 
FIGURE 1. Macroscopic presentation of squamous papilloma 
(Tumour 4).
FIGURE 2. Cytological presentation of mast cell tumours 
(Tumour 2). Hemacolor, 400 x.
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Racnik J et al. / Electrochemotherapy of tumours in ferrets100
tumour composed of round cells that exhibited 
mild anisocytosis. Neoplastic cells had a moder-
ate amount of pale blue cytoplasm and round nu-
clei that exhibited mild anisokaryosis. Additional 
Toluidine blue staining revealed numerous cyto-
plasmic metachromatic granules. Mitotic figures 
were rare. 
Cytological samples of the tumour 2 (Figure 2) 
contained moderate number of the neoplastic cells 
with the morphology similar to neoplastic cells in 
the tumour 1. Single eosinophils were scattered be-
tween neoplastic cells.
Histopathology of tumour 3 (Figure 3) exhibited 
epithelial tumour that formed papillary projec-
tions supported by a fine to moderate fibrovascular 
core. Papillary projections were covered with well-
differentiated squamous epithelial cells. Changes 
characteristic for papilloma, such as enlarged kera-
tohyalin granules, koilocytes and intranuclear in-
clusions, were not present. Mitotic figures were 6 
per 10 high power fields (HPF). The stroma was 
diffusely moderately infiltrated with neutrophils.
Histopathology of tumour 4 exhibited lobular 
tumour that consisted predominantly of cells with 
sebaceous differentiation (sebocytes) and periph-
eral layer of basaloid reserve cells. Sebocytes were 
round to oval, exhibited moderate anisocytosis and 
had finely vacuolated cytoplasm. Basaloid reserve 
cells were cuboid and had a small amount of baso-
philic cytoplasm, and round to oval nuclei. Mitotic 
figures were rare, 3 per 10 HPF, and confined to 
basaloid reserve cells. 
In the first patient, both masses were diagnosed 
as MCTs, and in the second patient, squamous 
papilloma of hock region and sebaceous adenoma 
of chest region were diagnosed. Haematology, 
serum biochemistry, total body radiographs, and 
abdominal ultrasound were performed for staging. 
Whole body radiographs and abdominal ultra-
sound investigations showed no evidence of health 
problems or distant metastasis. In the first patient, 
the haematology showed no abnormal findings, 
most of serum biochemistry values were within 
reference range; only urea nitrogen (12.4 mmol/L; 
reference 3.93–8.93 mmol/L9) and creatinine (128 
umol/L; reference 26.52–70.72 µmol/L9) were el-
evated suggesting early kidney disease. Also in the 
second patient, haematology results showed no 
abnormal findings; however, serum biochemistry 
showed elevated aspartate aminotransferase (248 
U/L; reference 78–140 U/L9) and decreased values 
of glucose (2.8 mmol/L; reference 5.5–7.5 mmol/
L9), most probably due to insulinoma and chronic 
gastroenteritis. The treatment possibilities, includ-
ing surgery, were discussed with the owner. Due 
to unsuitable locations for surgical treatment and 
contemporary morbidities, ECT was selected as the 
minimally invasive treatment option. The owners 
were thoroughly informed about the procedure 
and its possible side effects and signed informed 
consent for application of electrochemotherapy.
Electrochemotherapy
For the ECT, patients were anesthetised using iso-
flurane and 0.5 mg ~ volume of 0.1 ml of bleomy-
cin (3 mg/ml) was injected intratumourally using 
29 gauge needle (Figure 4, 5). After 1‒2 minutes, 
eight electric pulses of 100 µs duration with am-
plitude to electrode distance ratio of 1300 V/cm 
and frequency of 5 kHz were delivered using plate 
FIGURE 3. Histological presentation of squamous papilloma 
(Tumour 4). Hematoxylin and eosin stain, 100 x.
FIGURE 4. Intralessional injection of bleomycin into mast cell 
tumour (Tumour 2) located laterally on the right hock. Note the 
size of tumor and surgicaly chalenging anatomical location. 
Radiol Oncol 2018; 52(1): 98-104.
Racnik J et al. / Electrochemotherapy of tumours in ferrets 101
electrodes (distance between the electrodes: 6 mm) 
(Figures 6,7). Good contact between the electrodes 
and tumour mass was obtained by application of 
conductive gel to the treatment area. Electric puls-
es were generated by the electric pulse generator 
(CliniporatorTM - IGEA srl, Carpi [MO], Italy). The 
entire tumour was exposed to electric pulses by 
moving the electrodes perpendicular through the 
whole volume of mass and the surrounding skin, 
starting on the tumour periphery. The duration 
of each ECT cycle was approximately 15 minutes, 
and in both cases, the recovery from anaesthesia 
was uneventful. Meloxicam (Loxicom; Norbrook 
Laboratories) in a dose 0.2 mg/kg/day9 was pre-
scribed for 3 consecutive days orally after every 
cycle of ECT to reduce pain and inflammation.
Evaluation of response
After the treatment, the patients were examined at 
regular intervals, depending on the owner’s visit of 
clinic, to evaluate the treatment response. At each 
visit, the treated tumours were examined and pho-
tographed. In the meantime, the owner observed 
the treated area and reported the progress.
Results
No local or/and systemic side effects were noted 
during or after ECT. During ECT, some muscle 
contractions of the patients were observed after 
the application of each train of electric pulses. The 
contractions were mild, disappearing after the end 
of each train of electric pulses. All tumours be-
came necrotic and regressed. In the first patient, 
FIGURE 5. Intralessional injection of bleomycin into squamous 
papilloma (Tumour 4). 
FIGURE 6. Electric pulses were delivered to the mast cell tumour 
(Tumour 2) using plate electordes.
FIGURE 7. Electric pulses were delivered to the squamous 
papilloma (Tumour 4) using plate electordes.
Radiol Oncol 2018; 52(1): 98-104.
Racnik J et al. / Electrochemotherapy of tumours in ferrets102
the MCT located on the laterodorsal tail base be-
came necrotic on day 6 and a complete response 
(CR) was seen approximately 1 month after ECT, 
while the second MCT found on the lateral side of 
the right hock became necrotic on day 15 and CR 
was seen approximately two months (67 days) af-
ter ECT (Figure 9). In second patient, both tumours 
became necrotic on day 8 (Figure 8) and CRs were 
seen 70 days after ECT (Figure 10). In first patient, 
no tumour growth has been seen during the obser-
vation period of 15 months after ECT of the tumour 
located on the tail base, and 11 months after ECT of 
the tumour located on the right hock. In second pa-
tient, no tumour recurrence was detected 8 months 
after treatment. 
Discussion
ECT with bleomycin as a single treatment was an 
effective treatment of cutaneous neoplasms; MCTs, 
sebaceous adenoma, and squamous papilloma in 
our cases. ECT was well tolerated by the patients 
and is a minimally invasive procedure with no ma-
jor side effects noted, with excellent responses and 
long-lasting CR. In first patient, no tumour growth 
was seen during observation period of 15 months 
after ECT of the tumour located on the tail base, and 
11 months after ECT of the tumour located on the 
right hock. In second patient, no tumour regrowth 
was seen 8 months after treatment. Different stud-
ies reported an excellent treatment response of 
ECT with cisplatin or bleomycin in tumours of 
different histology with minimal side effects in 
dogs10,11, cats12, horses13, pet rats14, and reptiles15,16. 
In our cases, only some muscle contractions of the 
patient were observed during the application of 
electric pulses. The contractions were mild, disap-
pearing after the end of each train of electric pulses. 
In animals, pain during ECT can be avoided using 
sedation and/or general anaesthesia.10-16 Gaseous 
anaesthesia with isoflurane was used in our cases 
to prevent pain and facilitate proper position of 
patients for tumour manipulation, the applica-
tion of chemotherapeutic agent, and positioning of 
electrodes. Meloxicam, a nonsteroidal anti-inflam-
matory analgesic was prescribed to the patients 
before and after ECT to reduce pain and inflam-
mation.9 According to the literature, surgery with 
wide margins is advised as the first treatment op-
tion for benign skin tumours in ferrets2,5, but this 
therapeutic option is not always applicable due to 
anatomical locations. In author’s experience, some 
skin tumours could be quite large and located on 
toe, hock or footpad. Thus, aggressive surgery 
could result in loss of physiological function of a 
body part and a non-favourable cosmetic effect of 
therapy. In both ferrets, the tumour locations were 
not optimally positioned for surgery, and compli-
cations could arise with the skin defect too big for 
adequate closure. In that context, new therapies 
like ECT are highly beneficial, because of good an-
FIGURE 8. Necrosis with superficial scab of squamous papilloma 
(Tumour 4) 8 days after electrochemotherapy.
FIGURE 9. Complete response of mast cell tumour (Tumour 2) - 
67 days after electrochemotherapy.
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Racnik J et al. / Electrochemotherapy of tumours in ferrets 103
ti-tumour effectiveness, combined with excellent 
functional and cosmetic effects, while being less 
invasive than surgery.8,10,11,12 
Neoplastic diseases are commonly seen in fer-
rets, and medical treatment of tumours with chem-
otherapy is well reported.1,17,18 Different chemo-
therapeutic agents are used in ferret oncology, in-
cluding bleomycin.17,19 Bleomycin is an antitumour 
antibiotic commonly used in human and veteri-
nary medicine. In exotic pets, bleomycin was used 
intralesionally in the treatment of SCC in a greater 
hedgehog tenrec (Setifer setosus) and in a blue front-
ed amazon parrot (Amazona aestiva) for xanthoma, 
respectively.17 Recently, ECT with bleomycin was 
reported in a yellow bellied slider (Trachemys scrip-
ta scripta) and in a green sea turtle (Chelonia mydas) 
for the treatment of SCC and fibropapilloma with 
excellent therapeutic outcome and minimal side 
effects.15,16,17 In ferret oncology, the data about this 
chemotherapeutic agent are scarce; however, bleo-
mycin was used in the therapy of metastatic SCC 
in one animal at a dosage of 10‒20 U/m2 once a 
week, injected subcutaneously with moderate an-
titumour effectiveness.19 In our patients, ECT using 
bleomycin did not induce any clinically evident 
systemic side effects; only mild, local tumour ne-
FIGURE 10. Complete response of squamous papilloma 
(Tumour 4) - 70 days after electrochemotherapy.
crosis as a consequence of successful treatment was 
seen in the week following the treatment in both 
cases without notable effect on the patient’s condi-
tion. The superficial scab developed after necrosis; 
it fell off within few weeks after therapy. 
The drawback of our study is that it presents 
the ECT treatment effectiveness on only two pa-
tients. For broader acceptance of ECT in treatment 
of tumours in ferrets larger cohort of patients and 
higher number of tumours is needed. Though this 
study as the first provides evidence of safety and 
effectiveness of ECT in this specific animal species. 
In conclusion, ECT with bleomycin proved to be 
safe and effective against cutaneous MCTs, squa-
mous papilloma, and sebaceous gland adenoma 
in ferrets. Because of good effectiveness, low cost, 
and a relatively easy procedure ECT could repre-
sent a good treatment of choice instead of surgery 
for selected skin tumours in ferrets. 
Acknowledgment
The authors would like to thank Dr Aleksandra 
Domanjko Petrič, Clinic for Small animals, 
Veterinary faculty, University of Ljubljana and 
Dr Nina Mlakar Hrženjak, Clinic for Birds, Small 
Mammals and Reptiles, Institute of Poultry, Birds, 
Small Mammals and Reptiles, Veterinary Faculty, 
University of Ljubljana, for performing abdominal 
ultrasound for staging of disease in ferrets.
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