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Soft tissue Tumors

Fibroblastic / myofibroblastic tumors

Fibromatosis - deep (desmoid type)

Reviewer: Komal Arora, M.D. (see Reviewers page)
Revised: 20 July 2012, last major update July 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.


● Clonal fibroblastic proliferation of deep soft tissue with infiltrative growth
● "Desmos" (Greek) means tendon-like
● Locally aggressive (local recurrence, but no metastases)
● See also description at other sites, including breast, colon, small bowel


● Incidence of 2-4 per million population, less common than superficial fibromatosis
● May be familial (associated with Gardnerís syndrome/FAP syndrome, Clin Gastroenterol Hepatol 2008;6:215 or familial desmoid syndrome, Am J Hum Genet 1996;59:1193) or related to trauma

Clinical features

● Usually ages 15-39 years, may be painful
● Common sites in children are head and neck
● May be fatal due to local effects, particularly in head and neck
● Can be ďstagedĒ based on size, symptoms and complications (Dis Colon Rectum 2008;51:897)
● Prognostic factors: age, tumor size, tumor site (J Clin Oncol 2011;29:3553)

Abdominal fibromatosis:
● Arises within abdominal wall of women during or after pregnancy
● May see with cesarean section scar

Extraabdominal fibromatosis:
● Arises outside abdomen and abdominal wall, usually in muscles of shoulder, chest wall, back and thigh, equal gender frequencies

Intraabdominal fibromatosis:
● Mesenteric, pelvic or retroperitoneal locations, associated with Gardnerís syndrome (familial adenomatous polyposis, multiple osteomas)
● Often post-surgical

Case reports

● 27 year old woman with post-traumatic paraspinal mass (World J Surg Oncol 2008;6:28)
● 29 year old women with tumor of abdominal wall (Radiology 2005;236:81, Internet J of Surg 2007;10:2)
● 30 year old man with aggressive mesenteric tumor that responded to chemotherapy (Jpn J Clin Oncol 2008;38:222)
● 43 year old woman with tumor of retroperitoneal space (World J Surg Oncol 2004;2:33)


● Excision with wide margins and possibly frozen section evaluation of margins (Ann Surg Oncol 2009;16:1642)
● Inadequate excision may cause recurrence, less recurrence in abdominal wall than elsewhere but may recur 5-6 times
● May stop growing if stop excising, some recommend watchful waiting if asymptomatic or not growing (Expert Rev Anticancer Ther 2009;9:525)
● May respond to chemotherapy (J Clin Oncol 2007;25:501), COX2 inhibitors (Urology 2007;70:591.e3), imatinib (J Cancer Res Clin Oncol 2007;133:533), NSAIDs (World J Surg Oncol 2008;6:17), radiation (Am J Clin Oncol 2005;28:211), tamoxifen or watchful waiting (Eur J Surg Oncol 2008;34:462)

Clinical images

Swollen calf

Paraspinous subcutaneous mass

Site distribution in one study of 46 extra-abdominal desmoid tumors

Gross description

● Large, firm, white cut surface, infiltrative borders
● Often in muscular fascia, cuts with gritty sensation, 5-10 cm

Gross images

Extra-abdominal fibromatosis: dense white, trabeculated fibrous tissue that invades skeletal muscle and produces cross section of alternating white and red patches

Extraabdominal fibromastosis: thoracic tumor

Extraabdominal fibromastosis: firm white fusiform mass of calf

Abdominal fibromatosis: large tumor of anterior abdominal wall

Intraabdominal fibromatosis: retroperitoneal tumor has gray-glossy cut surface

Intraabdominal fibromatosis: mesentery of small bowel

Intraabdominal fibromatosis: retroperitoneal tumor has gray-glossy cut surface

Well defined margin (left-uncommon) versus infiltrative margin (right)

Desmoid fibromatosis (left) contrasted with high-grade fibrosarcoma (right);
fibromatosis has gristle-like consistency, but fibrosarcoma tends to be white, fleshy
and necrotic with an overlying tendon

Tumor infiltrates thoracic wall

Trunk tumor #1, #2

Thigh tumor

Gray-white tumor of Gardner syndrome

Micro description

● Poorly circumscribed with infiltration of adjacent tissue
● Uniform cellularity between exuberant fibrous proliferation and low grade fibrosarcoma
● Cells are bipolar fibroblasts and myofibroblasts (reduced amphophilic cytoplasm that merges with surrounding collagen, open chromatin, well defined nuclear membrane, one distinct nucleolus)
● Usually more collagenous and less cellular than nodular fasciitis
● Mucopolysaccharide matrix with thin walled, curvilinear, non-branching or ectatic vessels
● Stroma varies from collagenous, keloid-like to myxoid
● Regenerative muscle cells within lesions may resemble giant cells
● Perivascular lymphocytes at edge of lesion
● Few mitotic figures, no atypia
● Post radiation: histologic changes are minimal (Hum Pathol 2012 Mar 7 [Epub ahead of print])

Micro images

Extra-abdominal fibromatosis - AFIP:

Low power shows paucicellular fibrous proliferation in long fascicles, with numerous slit-like vessels characteristic of desmoid fibromatosis

Fibroblasts have spindled, dense, wavy nuclei and minimal cytoplasm

Margin shows infiltration of skeletal muscle, a common feature

Atrophic and regenerating muscle fibers at the edge of the lesion may resemble rhabdomyoblasts

Some tumors are myxoid

Cells in myxoid tumors are uniformly bland, unlike those in malignant myxoid tumors

Cellular tumor has scattered mitotic figures, none atypical

Keloid-type pattern may be observed focally in deep tumors

Extra-abdominal fibromatosis - other sources:
Paraspinal tumor

Thigh mass has spindle cells, dense collagenous stroma, slit-like vessels and chronic inflammation

Pre-radiation therapy

Post-radiation therapy shows reduced cellularity

Breast tumor is smooth muscle actin+

Intra-abdominal (mesenteric) fibromatosis - AFIP:

Tumor appears to be extrinsic to bowel muscularis propria, which distinguishes it from GIST

Fibromatosis is paucicellular and composed of relatively uniform, bland spindle cells

Bland, mitotically active, uniform cells in myxoid stroma

Less commonly bland spindle cells are within collagen bundles

Pelvic tumor

Trichrome stain highlights collagen in the fibromatosis and distinguishes it from overlying normal muscularis propria

Intra-abdominal fibromatosis - other sources:
Uniform spindle cells with moderate collagen

Abdominal fibromatosis:

Extension into adjacent muscle

Fascicles of fibroblastic spindle cells with abundant intercellular collagen



● Bland spindle cells with long, fusiform nuclei and metachromatic matrix material
● Tumor cells are individual or as fragments within matrix (Cancer 2007;111:166)
● FNA is fairly reliable for diagnosis but core needle biopsy is better (Acta Orthop 2006;77:926)
● May have long fascicular arrangement of spindle cells (Diagn Cytopathol 2012;40:45)

Cytology images

Low power shows paucicellular fibrous proliferation in long fascicles, with numerous slit-like vessels characteristic of desmoid fibromatosis

Positive stains

● Vimentin, variable smooth muscle actin and muscle specific actin, variable CD117 (Am J Surg Pathol 2002;26:1296, but depends on antibody used, Am J Surg Pathol 2001;25:549)
● Also nuclear beta-catenin (sensitive but not specific, Am J Surg Pathol 2005;29:653, Am J Surg Pathol 2002;26:1296), ER-beta (Cancer 2006;106:208, Biosci Trends 2010;4:25)

Negative stains

● Keratin, S100, CD34 (J Clin Pathol 2004;57:1119)
● ALK, desmin, ER-alpha, c-Kit, PR (J Clin Pathol 2005;58:1152)

Electron microscopy description

● Fibroblastic and myofibroblastic features, including intrareticular collagen fibers, thin filament bundles, cytoplasmic dense bodies


● Clonal; associated with Wnt/beta-catenin (APC-beta-catenin-Tcf) pathways
● Somatic beta-catenin point mutations in exon 3, codon 41 or codon 45 in 87% (Am J Surg Pathol 2007;31:1299)
● Also associated with trisomy 20 and 8 (Am J Path 1999;154:729, Cancer Genet Cytogenet 1995;79:139) and loss of 5q (APC gene)

Molecular images

Trisomy 20 and 8

Differential diagnosis

● Fibrosarcoma: atypia or mitotic figures present
● GIST: strong CD117+, CD34+, Am J Clin Pathol 2004;121:93)
● Idiopathic retroperitoneal fibrosis (Ormanís disease): inflammatory, strangles the ureters
● Leiomyoma: bright pink cytoplasm of smooth muscle, desmin+
● Low grade fibromyxoid sarcoma: heavily collagenized stroma with abrupt transition to myxoid areas, often epithelioid areas or poorly formed but large collagen rosettes; beta catenin negative
● Neurofibroma: no myofibroblasts, S100+
● Schwannoma: palisading Schwann cells, usually minimal collagen, S100+
● Sclerosing omentitis: grows like panniculitis, beta catenin negative

End of Soft Tissue Tumors > Fibroblastic / myofibroblastic tumors > Fibromatosis - deep (desmoid type)

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