Fibrosarcoma
Fibrosarcomas are bland-appearing, firm white tumors and by microscopic examination are composed of sheets of bland appearing spindle shaped cells. It is very important to have such tumors examined by knowledgeable pathologists versed in the diagnosis of sarcomas, given the difficult in discerning them from other important types of sarcomas. In fact, fibrosarcoma is a diagnosis of exclusion, once the possibility of malignant peripheral nerve sheath tumor, myxofibrosarcoma, desmoid tumor, or synovial sarcoma (among others) has been ruled out.
Epidemiology
Fibrosarcoma is increasingly rare as a diagnosis compared to other sarcoma subtypes. In older literature, any sarcoma with fibroblasts was termed a fibrosarcoma, and represented two-thirds or more of all sarcomas. In the last 20 years the diagnosis of fibrosarcoma has become much more rare, with better ways of studying tissue such as immunohistochemistry (testing of specific proteins within tumors) and cytogenetics (analysis of chromosomes). Many of these tumors are now termed “MFH” for malignant fibrous histiocytoma, which itself has been renamed “undifferentiated pleomorphic sarcoma” in the latest guide to sarcomas from the World Health Organization (WHO).
Based on data from Memorial Hospital from a database from 1982 to present of patients operated on at that hospital, these tumors comprise approximately 10% of all sarcomas. Their prognosis may be better than that of other sarcomas, perhaps because they are found to be lower grade (less aggressive) than other sarcomas of comparable size, and tend to occur at a slightly younger age than other sarcomas, with a peak incidence between ages 30 and 40.
Distinct Clinical Features
Some forms of fibrosarcoma are unique in terms of their biology. For example, Evans’ tumor is a form of fibrosarcoma (low grade fibromyxoid sarcoma), which looks to be a non-aggressive form of sarcoma under the microscope, but behaves badly and frequently travels elsewhere in the body in the form of metastases. Sclerosing epithelioid fibrosarcoma has some features of more common cancers (carcinomas) in terms of the cells seen within the fibrous background of the tumor, which can make ruling out another diagnosis very difficult.
Treatment and Follow-up for Localized Disease
Treatment for fibrosarcoma remains focused on treatment of the primary tumor. Surgery is the only curative treatment for these tumors available, and radiation is often used when the tumor measures at least 5 cm (2 inches) in size. The use of chemotherapy after surgical removal of the original tumor to try and destroy microscopic undetected metastatic disease to other parts of the body (adjuvant chemotherapy) remains controversial.
Like all sarcomas, the risk of recurrence after surgical treatment depends on the stage of disease. For sarcomas that are localized, low grade sarcomas are stage I, and large, high-grade, deep sarcomas are stage III. If a sarcoma does not have all three features (large, high-grade, and deep), it is stage II. Sarcomas that have traveled to lymph nodes or other sites of the body beyond where they started are considered stage IV, or metastatic, disease.
Treatment and Follow-up for Metastatic Disease
If fibrosarcoma forms metastases, such metastases are usually located in the lungs. If the tumors cannot be easily removed from the lungs surgically (typically when there are multiple tumors or if they are found in difficult locations in the lungs) then chemotherapy is used in an attempt to control the tumor. A standard chemotherapy drug, such as doxorubicin (in its regular form, or in an encapsulated form called Doxil or Caelyx) is frequently used for metastatic disease, and ifosfamide chemotherapy with the bladder protectant mesna is often used as well. Dacarbazine (DTIC) can be considered for treatment of these tumors, as can other commercially available drugs not specifically approved for sarcomas, such as the combination of gemcitabine and docetaxel. In this setting, when available, new medications under study can be used either before or after use of standard chemotherapy drugs in clinical studies, available from an increasing number of institutions.
Targeted Therapies
There is presently no specific “targeted” therapy against fibrosarcoma because we have not identified proteins unique to fibrosarcomas that could be used as targets for such treatment. However, it is expected that new drugs available for other soft tissue sarcomas will be used for fibrosarcomas as well.