Radiation Oncology Synopsis

Desmoid Tumors
(Aggressive Fibromatosis)

Overview

Desmoid tumors belong to myofibroblastic fibromatoses. They are unusual in their bland histology and slow progression. Surgery remains the treatment of choice for these lesions. They are clinically diverse deep seated fibrous neoplasms, but are not true sarcomas as they lack the potential to metastasize. They are divided into 3 main biologic groups:

Desmoids were originally noted to be associated with tumors of the abdominal wall in post partum women. They can arise anywhere in the body. There are three main subsets:

Site affects management, but site does not appear to be biologically significant. They are called aggressive fibromatosis especially in the retroperitoneum due to their potential for invasion and progressive growth. They do not metastasize but do form large infiltrative masses which recur repeatedly if not excised completely. Wide local excision must be balanced by preservation of function. They can be controlled with low dose chemotherapy or NSAIDs. Occaisionally they regress spontaneously.

Abdominal and retroperitoneal desmoids are more common in patients with FAP/Gardiner's syndrome. Gardiner's is linked to the APC gene on 5q. Other tumors associated with FAP/Gardiner's are fibromas, osteomas, and epidermoid cysts.

Treatment

Surgery

Surgery is the mainstay of treatment of desmoid tumors. The role of radiation for completely resected desmoid tumors is controversial. Most agree that for patients with negative resection margins, postoperative radiation therapy is not recommended

Radiation

For patients with microscopic margins, the role of radiation in more debatable. Spear reported local control of 61% for primary tumors with positive margins treated with surgery alone, but most report lower local control rates. The conclusion is that failure does not inevitably occur if residual microscopic tumor remains, and these lesions can be watched, as long as local progression does not coause significant morbidity. When adjuvant radiation is indicated for some primary and most recurrent tumors, then 50 Gy is given usually. Indications for radiation therapy postoperatively are: recurrence after resection to a total dose of 50 Gy, following re-resection.

Advanced desmoids in the abdomen can cause significant morbidity in the proximal extremity and can be lethal if they arise in the retroperitoneum because they are difficult to completely resect.

Definitive radiation is emerging as a reasona ble alternative to radical surgery with 5 year local control rates of 69% reported for gross disease. The recommended dose is 56 Gy at 2 Gy/fraction or 60 Gy at 1.8 Gy/fraction.

Pharmaceutical/Hormonal Management

Desmoids were classically identified as arising in pregnancy as an extra-uterine abdominal mass. Desmoids have been noted to have estrogen binding sites in some cases. There are anecdotal reports of response to tamoxifen and GNRH agonists or aromatase inhibitors.

There are well documented responses to sulindac and other NSAIDs. Responses are slow, and can take months and can continue for years.

Chemotherapy

Response have been reported to doxorubicin and combination at standard or low doses. Responses are slow. Therapy should not be abandoned for stable disease. Reports of complete resonses are exceptionally rare.