II. Lymphosarcoma
III. Miscellaneous Neoplastic Diseases
The most common tumor of rabbits is the uterine adenocarcinoma.
Females with this tumor have a history of reproductive disturbance prior
to detection of the tumor. Fertility is diminished, litter size is
reduced, stillbirths are more numerous, and desertion of the litter by
the doe is common. Other symptoms are dystocia, fetal retention
in utero, abdominal pregnancy, and fetal resorption. The
period of altered reproductive function precedes tumor detection by 6 to
10 months. The duration in time between clinical detection and death
(usually post-metastasis) is 12 to 24 months. Uterine nodules can
be palated or observed on radiographs or laparatomy.
Histologically, the events of the tumor progression are characterized
by increasing degrees of epithelial cell dedifferentiation and anaplasia
with increase of the vascular, myxoid stroma. There is loss of cellular
elements such as cilia and secretory vesicles. Areas of necrosis
are not uncommon in mature tumors. The incidence of neoplasia is
most common in New Zealand rabbits but has been observed in other rabbit
breeds. Ovariohysterectomy is the preventative measure that not only
eliminates the source of the most common cancer, but also prevents the
undesirable behavioral changes that often accompany sexual maturity in
pet does.
The second most common rabbit neoplasm is the lymphosarcoma. Susceptibility
to the disease is believed due to an autosomal recessive gene expressed
in the homozygous state. It is considered a tumor of juvenile and
young adult rabbits. A tetrad of necropsy lesions considered pathognomonic
for lymphosarcoma in the domestic rabbit are 1) enlarged kidneys, light
tan in color with irregular lumpy surface, and thickened cortex but normal
medulla; 2) hepatomegaly with a diffuse pattern of small pale foci; 3)
splenomegaly; and 4) lymphadenopathy, in which all of the lymph nodes in
the body may be involved in the neoplastic process. Histologically,
the normal architecture of the nodes is obliterated by masses of infiltrating
neoplastic lymphoblasts. 
III. Miscellaneous Neoplastic Diseases
Other commonly reported tumors of the rabbit are embryonal nephromas,
bile duct adenomas, mammary gland papillomas, mammary adenocarcinomas,
and squamous cell carcinoma. The latter tumor has been mentioned
previously in conjunction with Shope papilloma virus (SPV). One type
of squamous cell carcinoma occurs if the SPV produces a papilloma that
lasts over 200 days. At this point, spontaneous change from papilloma
to squamous cell carcinoma occurs. Other tumors also caused by oncogenic
viruses (Shope fibroma virus, oral papilloma virus, and myxoma virus) have
already been discussed. Some other tumors that have been reported
infrequently in the rabbit include tumors of the endocrine glands, melanomas,
plasma cell myelomas, thymomas, osteosarcomas, osteochondromas, renal carcinomas,
basal cell adenomas, leiomyomas, and leiomyosarcomas.
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