Myxoid sarcoma or myxosarcoma in rabbits
Esther van
Praag, Ph.D.
Warning: this file contains pictures
that may be distressing to some persons
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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, head, neck, shoulder, chest,
abdomen or hip; as well as in all types of tissues: muscle tissue, fat
tissue, in the blood vessels, in the tissue surrounding joints, and in
tendons. 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. • Vascularization:
malignant tumors are rich in blood vessels, whereas benign tumors are
avascular or poorly vascularized. Sarcoma tumors are locally invasive into the surrounding tissues.
Although their metastatic rate is low, they can metastase
through the bloodstream to other organs. Myxosarcoma is defined has a
fibrosarcoma rich in connective tissue proteoglycans
(mucins). This kind of tumor is therefore also
sometimes called myxoid fibrosarcoma. In veterinary medicine, the term
“myxosarcoma” remains, however, a general term for otherwise specific sarcoma
tumors like myxofibrosarcoma, liposarcomas or
malignant fibrous histiocytomas. A virus called "malignant
rabbit fibroma virus" has been isolated in rabbits, which can lead to
fibrosarcoma, and perchance to fibrosarcoma derived myxosarcoma. See: “Fibrosarcoma in rabbit” Diagnosis and
histology
The
nature of the mass and the presence of metastases must be determined, by
means of X-ray, ultrasound, and a biopsy.
Myxosarcoma differentiate between low-grade, intermediate and
high-grade lesions. The tumors can be small and (multi)nodular, or large.
Their degree of malignancy is generally low, but increases with successive regrowth (recurrence). All have invasive properties into
surrounding tissues.
Typically, a tumor has a
myxoid matrix containing spindle- to polyhedral cells. The neoplastic cells
can have various shapes: round, ovoid or elongated; their nuclei is hyperchromatic. Sheets of interdigitated
cells, rich in myxoid matrix can be present. Pseudolipoblasts
are commonly observed. Vascularization of the tumor is typical, with
curvilinear capillaries. A low-grade myxosarcoma must be differentiated from a benign
myxoid lesion.
Treatment
The complete excision of the myxosarcoma lesions is necessary.
Indeed, a characteristic of myxosarcoma and myxofibrosarcoma tumors is their
high rate of recurrence (according to species, up 70% within year of surgical
removal). At recurrence, these lesions gain a higher grade of aggressiveness
and an increased potential to become malignant. The prognosis is therefore
guarded.
For detailed
information on myxosarcoma in rabbits, see: “Skin
Diseases of Rabbits”, by E. van Praag, A. Maurer
and T. Saarony, 408
pages, 2010.
Acknowledgements
All my gratitude to Susan L. (USA), to Christine Harvey, DVM (USA),
to E. Kufuor-Mensah, DVM (USA) and to Dr. Taylor,
DVM (USA) for kindly allowing the use of illustrative material for this text.
Thanks are also due to Timothy, 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. Richardson
V., Rabbits: Health, Husbandry and Disease, Blackwell Science Inc 2000. Schaff Z, Grimley PM, Michelitch J, Banfield WG.
Spontaneous myxosarcoma in a cottontail rabbit (Sylvilagus floridanus): observation of tubular structures in the
endoplasmic reticulum of tumor cells. J Natl Cancer
Inst. 1973; 51(1):293-7. Strayer DS, Sell S, Skaletsky E, Leibowitz JL. Immunologic
dysfunction during viral oncogenesis. I.
Nonspecific immunosuppression caused by malignant
rabbit fibroma virus. J Immunol. 1983;
131(5):2595-600.. |
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