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616.e2 Malignant Fibrous Histiocytoma

Malignant Fibrous Histiocytoma Client Education
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moderate metastatic potential, but some
BASIC INFORMATION
variants or grades may be more likely to tumors usually have a different prognosis
and recommended course of treatment.
Definition metastasize (see Prognosis & Outcome ○ Histopathologic grade of the tumor is
An uncommon primary tumor made up of below). necessary for determining the prognosis
fibrous and inflammatory cells is thought • Lesions caused by malignant fibrous histiocy- and treatment of most soft-tissue sarcomas.
to arise from a primitive mesenchymal cell. toma depend on the location of the primary ■ Histopathologic grading typically
It may be difficult to differentiate from tumor. involves using the general grading
malignant histiocytosis (histiocytic sarcoma), • These tumors are considered a separate entity system for soft-tissue sarcomas based
a disease of localized or multisystemic histiocytic from the other histiocytic diseases but may be on mitotic rate, percent necrosis, and
infiltration. difficult to differentiate from them (p. 473). degree of differentiation.
Peripheral tumors can metastasize, usually ■ Tumors are graded as low, intermediate,
Synonyms to the lungs. or high grade.
Epithelioid sarcoma, giant cell fascial sarcoma, ■ In most cases, high-grade tumors are
giant cell tumor, reticulum cell sarcoma DIAGNOSIS larger and more invasive, but gross
Epidemiology Diagnostic Overview size and invasiveness cannot be used
as a substitute for histopathologic
SPECIES, AGE, SEX Definitive diagnosis can be confirmed only grading.
• Malignant fibrous histiocytoma is an uncom- by histopathologic analysis, although addi-
mon tumor of the skin and subcutaneous tional testing such as diagnostic imaging is TREATMENT
tissue of dogs and cats that also can occur often helpful in defining the extent of the
in the spleen in dogs. tumor. Treatment Overview
• This tumor type has been reported at injec- • Definitive treatment is based on complete
tion sites in cats. Differential Diagnosis eradication of the primary tumor whenever
• Other skin and subcutaneous tumors possible.
GENETICS, BREED PREDISPOSITION ○ Soft-tissue sarcoma • Additional treatment such as chemotherapy
Golden retrievers and rottweilers may be ○ Mast cell tumor may be indicated to prevent or delay metas-
overrepresented. ○ Others (p. 628) tases or in dogs with high-grade tumors, the
• Other splenic tumors giant cell variant of this tumor, or tumors
Clinical Presentation ○ Hemangiosarcoma that have already metastasized.
DISEASE FORMS/SUBTYPES ○ Lymphoma • Palliative treatment options, such as palliative
Different pathologic types include storiform- ○ Others (p. 629) radiation, may help control pain or discom-
pleomorphic, inflammatory, and a giant cell fort in patients with advanced tumors or in
variant. The giant cell variant, which occurs Initial Database patients where definitive treatment cannot
in dogs but is rare in cats, is associated with • Fine-needle aspiration and cytologic analysis be tolerated.
metastasis and a poor prognosis. can help identify the tumor type before other • Palliative radiation or metronomic chemo-
diagnostics. therapy (daily low doses of chemotherapy)
HISTORY, CHIEF COMPLAINT • Three-view thoracic radiographs to rule out may help control the local tumor for
• Pets with malignant fibrous histiocytomas pulmonary metastases significant periods.
in the skin and subcutaneous tissue usually • Radiographs of the affected area may reveal
present for a progressively enlarging mass involvement of underlying bone. Acute and Chronic Treatment
noticed by the owner. • Abdominal ultrasound can identify splenic • Aggressive surgical resection, radiation
• Dogs with malignant fibrous histiocytomas tumors and rule out metastasis but cannot therapy, and/or chemotherapy may be used
of the spleen usually present for signs be relied on to differentiate malignant for treatment.
related to an abdominal mass or abdominal fibrous histiocytoma from other splenic • Chemotherapy may be indicated to delay
hemorrhage. tumors. or prevent metastasis for malignant fibrous
• Fine-needle aspiration of draining lymph histiocytoma affecting the spleen, high-grade
PHYSICAL EXAM FINDINGS nodes to help rule out metastasis tumors, or giant cell variants of malignant
• Malignant fibrous histiocytomas in the fibrous histiocytoma.
skin and subcutaneous tissue often present Advanced or Confirmatory Testing
as firm, palpable masses. Occasionally, they • CT or MRI may be necessary to delineate Possible Complications
are hairless or ulcerated. the local extent of the tumor and plan for Complications of treatment depend on the
• Regional lymphadenomegaly may be second- surgery or radiation therapy. types of treatments and location of the primary
ary to inflammation or (rarely) lymph node • Biopsy: diagnosis of malignant fibrous tumor.
metastasis. histiocytoma is based on histopathologic
• Dogs with splenic tumors may present evaluation of tissue. Recommended Monitoring
with abdominal mass, pain, or abdominal ○ Special stains may be necessary to dif- After appropriate local treatment, follow-up
enlargement. ferentiate malignant fibrous histiocytoma exam should be done routinely to monitor for
from other soft-tissue sarcomas, especially recurrence (every 2-3 months) and metastasis
Etiology and Pathophysiology poorly differentiated tumors. (thoracic radiographs at 6 months and 1 year).
• Malignant fibrous histiocytomas are typically ○ Care should be taken to differentiate High-grade tumors may require more frequent
firm, slow-growing tumors that commonly these tumors from other histiocytic monitoring (at least every 2-3 months) for
infiltrate into surrounding soft tissues and tumors, including histiocytic sarcoma metastases during and after chemotherapy
along fascial planes. Overall, they have a and malignant histiocytosis. The other administration.

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