Page 1362 - Small Animal Internal Medicine, 6th Edition

1334 PART XII Oncology

As a general rule, surgery is indicated for cats with a soli- the right shoulder, a high proportion of tumors still develops
tary cutaneous mass, for cats with two to five skin masses, in the interscapular region (Shaw et al., 2009). Current vac-
VetBooks.ir and for cats with intestinal or splenic involvement. As dis- cination protocols for cats should be evaluated by general
practitioners, so that safe vaccination practices are routinely
cussed previously, cutaneous MCTs in cats are less aggressive
than in dogs, and in most affected cats, removal of a solitary
ican Association of Feline Practitioners (AAFP) guidelines).
dermoepidermal MCT using a biopsy punch is curative; the used (see Recommended Reading for the most recent Amer-
same applies to cats with fewer than five dermoepidermal A rapidly growing soft tissue mass develops in the region
MCTs. Cats with splenic MCT can have prolonged survival weeks to months after vaccination or injection in cats with
times when undergoing splenectomy, even if metastatic ISSs. A vaccine- or injection-associated inflammatory reac-
disease is present at the time of treatment, with survival tion may precede the development of this neoplasm. There-
times over 1 to 2 years recently reported (Kraus et al., 2015). fore an ISS should be suspected in any cat with a superficial
In the more recent study, there was no definitive benefit seen or deep mass in the interscapular or thigh regions, and every
in cats that received chemotherapy following splenectomy; effort should be made to establish a diagnosis immediately.
however, cats that did not undergo splenectomy had a sig- The current recommendation is to use the “3, 2, 1 Rule”:
nificantly shorter survival than cats those who were splenec- worry if the mass persists for more than 3 months after vac-
tomized. If chemotherapy is pursued, the most common cination, is larger than 2 cm in diameter, or grows 1 month
agents tend to be corticosteroids (prednisone, dexametha- after the injection.
sone), alkylating agents (chlorambucil, lomustine), vinblas- Although FNA findings may provide a definitive answer,
tine, or TKIs. Cats with intestinal MCTs are generally treated more often an incisional or needle biopsy is necessary
with surgery and/or chemotherapy, and initial survival times because sarcomas do not consistently exfoliate cells (see
were shown to be quite poor due to the presence of meta- Chapter 71). However, excisional biopsies are not recom-
static disease in many cats. However, recently, a larger study mended, as shorter survival times may be seen in cats that
reported an overall MST of 1.5 years in cats treated with a have undergone an excisional biopsy prior to definitive
variety of chemotherapy, surgery, or steroids alone, so more treatment.
prolonged survivals may be possible even without surgery Although most FSAs in dogs and cats have a low meta-
(Barrett et al., 2018). static potential, ISSs are quite aggressive and should be
2
We recommend using chlorambucil (20 mg/m , PO, q2 treated accordingly. Although multiple studies are currently
weeks) with or without dexamethasone (4-5 mg total dose, in progress, on the basis of the results of studies reported in
q1-2 weeks, PO or subcutaneously) after splenectomy or the literature and on the findings in cats seen at the author’s
intestinal MCT removal in cats with systemic disease. In clinic, the rate of metastases of ISSs can be high (probably as
most cases, survival times of 1 to 2 years are common. high as 50%-70% in cats with recurrent tumors). Pulmonary
metastatic lesions can be detected at presentation in up to
20% of cats with ISSs.
INJECTION SITE SARCOMAS IN CATS The treatment of choice for cats with ISS is aggressive
surgical excision (see Chapter 75). In keeping with the maxim
An association between injections/vaccination and the “cut it once, but cut it all,” an en bloc resection (to include
development of sarcomas has been recognized in cats since any biopsy tracts) should be performed immediately after
the early 1990s, and epidemiologic studies have confirmed the diagnosis is established, provided there is no metastatic
the association. In this syndrome, fibrosarcomas (FSAs) or disease (Phelps et al., 2011). Cats treated with aggressive
other types of sarcomas develop in the subcutis or muscle surgery have significantly longer disease-free survival times
in the interscapular region or the thigh, common sites than cats treated with conservative surgery (274 versus 66
of injection/vaccination. It is estimated that a sarcoma days); also, cats with tumors in the limbs have significantly
develops in 1 to 2 of 10,000 cats that receive an injection. longer disease-free survival times than cats with tumors in
Although the exact pathogenesis is still unclear, both the the trunk (325 versus 66 days; Hershey et al., 2000). Cats
adjuvants and the local immune response against the anti- that experience local recurrence after the first aggressive
gens (i.e., inflammation) have been implicated as causative surgery have significantly shorter MSTs than those without
agents. A recent epidemiologic study reported that cats recurrence (365 versus 1100 days [Romanelli et al., 2008]
with injection site sarcoma (ISS) had a higher probability and 499 versus 1461 days [Phelps et al., 2011]); as expected,
of having received long-acting corticosteroid injections in cats with metastases at presentation also have shorter MSTs
the interscapular region, whereas cats with rear limb ISS than those without distant metastases (165 versus 930 days
were significantly less likely to have received recombi- [Romanelli et al., 2008] and 388 versus 1528 days [Phelps
nant vaccines than inactivated vaccines (Shrivastav et al., et al., 2011]). Complete surgical excision of a relatively
2012). small ISS (i.e., <2 cm in diameter) is usually associated with
Despite changes in vaccination recommendations in 2001 long-term remissions and even cure. Although the role of
to administer rabies vaccine in the right rear leg as distally as postoperative adjuvant chemotherapy has not been thor-
possible, the feline leukemia virus (FeLV) vaccine in the left oughly evaluated, cats with large or incompletely excised
rear leg as distally as possible, and the FVRCP±C vaccine in tumors may benefit from treatment with mitoxantrone and