498 DISEASES/DISORDERS
Histopathologic evaluation of the entire excised tissue: essential to determine surgical
margins and to predict biologic behavior; recommend 2–3 cm lateral margins and one
fascial plane deep to the mast cell tumor if possible; perform aggressive excision as
soon as possible post diagnosis.Although incomplete excision may leave residual tumor, some reports indicate that
incompletely excised grade 1 and 2 tumors may not regrow.
Lymph node involvement but no systemic involvement: aggressive excision of the
affected lymph node(s) and the primary tumor required; follow-up chemotherapy
useful to prevent further metastasis.Primary tumor and/or affected lymph node cannot be excised: chemotherapy has min-
imal benefit.
Systemic metastasis: excision of primary tumor and affected lymph nodes and follow-
up chemotherapy have minimal effect on survival time.
Radiotherapy: external beam radiation therapy: excellent adjuvant option for unre-
sectable tumors; if possible, debulk tumor prior to radiotherapy; tumors on an
extremity respond better than do tumors located on the trunk.Cats
Surgery: treatment of choice for cutaneous tumors.
Some forms will spontaneously regress.
Cats should be staged to insure that they do not have splenic primary mast cell tumor
that is metastasizing to cutaneous locations as well as other sites.
Drugs of Choice
Chemotherapy is typically less effective than surgery and radiation therapy; regardless
of response rate, median time to progression 77–141 days.
Prednisolone: induced remission and prolonged survival time in 20% of patients with
grade 2 or 3 tumors; only one of the five responding patients had documented lymph
node metastasis when initiated.Chlorambucil/prednisolone: overall response rate 38%.
Lomustine: overall response rate 42%.
Vinblastine/prednisolone: overall response rate 47%.
Vinblastine/lomustine/prednisolone: overall response rate 65%.
Vincristine alone: partial remission in 21% of patients.
Studies suggest that lomustine, vinblastine, and cyclophosphamide have limited
activity against mast cell tumors; may lengthen time of remission with prednisone-
sensitive tumors. Dogs:
Prednisolone: 1 mg/kg PO q24h; taper slowly after 4 months; discontinue after
7 months
Vinblastine alone: 3.5 mg/m (^2) IV q14 days; partial remission 21%
Vinblastine 2 mg/kg/m (^2) IV q7 days for four treatments; then q14 days with pred-
nisolone 1 mg/kg PO q24h