Fibrosarcoma in rabbits
Esther van
Praag, Ph.D.
Warning: this file
contains pictures that may be distressing to some persons
The word “sarcoma” comes from
the Greek and means “fleshy growth”. Sarcoma is nowadays used to describe
relatively rare a group of malignant tumors that involve the connective tissue.
Although sarcomas are well-recognized tumors, their characteristics lead to
confusion. Indeed, some type of sarcoma may present a combination of features
of various different types of sarcoma. This lead to the widely accepted
conclusion that the neoplastic development of a primitive mesenchymal cell
can lead into different direction, thus different types of sarcoma. The tumors are found is all
parts of the body: forelimbs, hind limbs, chest, and abdomen; as well as in
all types of tissues: muscle tissue, nerves, tendons, scar tissue, bones and
their lining. Four principles apply for sarcoma tumors: • Location: a
superficially located tumor is less likely to be malignant than a deeper
located tumor; • Size: bigger tumors are
more likely to become malignant than small tumors; • Growth: rapid growth tumors are more likely to be malignant
than slow growing ones. Fibrosarcoma seems more
frequent in rabbits as generally assumed. These mesenchymal tumors are
aggressive, have generally a rapid growth rate and are invasive into
surrounding tissues, e.g. muscle or periosteum (tissue lining bones).
Indirect invasion of transport of a metastatic cell via the blood stream is
possible and metastasis can form in the lungs, heart, kidneys and lymph
nodes. A virus called "malignant
rabbit fibroma virus" has been isolated in rabbits and can lead to
fibrosarcoma. It presents antigenic similarities with the fibroma and myxoma
viruses, it is thought to be a recombinant of both viruses, but this is not
yet well defined. The presence of this virus is accompanied by
immunodepression, malignant tumors and infections. In rare cases, the fibrosarcoma can present myxoid features and
will develop into a myxosarcoma. See: “Myxoid sarcoma or myxosarcoma in rabbits” Diagnosis and
histology
The nature of the mass and the presence of metastases must be
determined. This can be done by X-ray, ultrasound, and a biopsy.
Fibrosarcoma are heterogenous.
The presence of “fishbone-shaped”
fusiform cells within a collagenic stroma is characteristic and
characteristic for a neoplasm of mesenchymal origin. Numerous cells are
undergoing mitosis. Necrotic or hemorrhagic foci are commonly observed.
Treatment
The complete excision of the fibrosarcoma
lesions is necessary. If a limb is affected, amputation is the option of
choice. Chemical treatments have been administered to rabbits suffering from
fibrosarcoma, in order to reduce the size of the tumor in rabbits. Rabbits
should be closely monitored after each treatment, as the drugs can affect the
bacterial flora of the intestine and cause severe diarrhea. Treatment 1: • 1 mg/kg adriamycin IV
q. 3 weeks, through peripheral catheter, • Cytoxan:
standard cat dose 4 days/week, PO • L-asparaginase
(Elspar): standard cat dose, • 2mg/kg prednisone
daily. Treatment 2: • Prednisone and L-asparaginase (Elspar) alone. A characteristic of fibrosarcoma tumors is their high rate of
recurrence (according to species, up 70% within year of surgical removal).
For detailed information
on fibrosarcoma in rabbits, see: “Skin
Diseases of Rabbits”, by E. van Praag, A. Maurer
and T. Saarony, 408
pages, 2010. Acknowledgements
Thanks are due to C. Harvey, DVM (USA), Susan L. (USA), Jeff Hymel (USA), and Juliet Brown (Australia) for providing
the illustrative material for this text. Thanks are also due to Sparky and
Atticus, for his patience during picture-sessions. Further
information
Flecknell P., editor Gloucester, BSAVA Manual of
Rabbit Medicine and Surgery, UK: British Small Animal Veterinary
Association2000. Hillyer E.V. and Quesenberry
K.E., Ferrets, Rabbits, and Rodents: Clinical Medicine and Surgery, New York:
WB Saunders Co.1997. Janssens G, Simoens P, Muylle S, Lauwers H. Bilateral
prolapse of the deep gland of the third eyelid in a rabbit: diagnosis and
treatment. Lab Anim Sci. 1999; 49(1):105-9.
Manning P.J., Ringler D.H., Newcomer C.E., The Biology of the Laboratory Rabbit, New
York: Academic Press1994. Renfrew
H, Rest JR, Holden AR. Extraskeletal fibroblastic osteosarcoma in a rabbit (Oryctolagus cuniculus). J Small Anim Pract. 2001; 42(9):456-8. |
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