Microscopic description:

Spindle cell large tumor involves the full thickness of the small bowel with focal cystic change and bowel perforation. Long sweeping fascicles with elongated, slender, spindled cells of uniform appearance and pale cytoplasm set in a collagenous stroma. No nuclear hyperchromasia, minimal cytologic atypia and variable mitotic rate (typically low but may be focally increased). The tumor features focal keloid-like areas. On IHC, the tumor cells are diffusely positive for beta-catenin (nuclear staining), focally positive for SMA and desmin, while negative for CD117, DOG-1 and S100. The findings support the above diagnosis of mesenteric desmoid-type fibromatosis.

Discussion:

Locally aggressive fibroblastic / myofibroblastic tumor arising in deep soft tissues with no metastatic potential.

Extraabdominal tumors are deep seated, poorly circumscribed and painless.

Abdominal wall tumors typically arise in gravid or postpartum women.

Intraabdominal tumors arise as slowly growing, painless masses that may mimic ovarian tumors.

Local recurrence in 20 - 30%.

Highly variable natural course, with up to 25% undergoing spontaneous regression.

Increasing tendency to follow with observation only.

Mainstay of treatment is surgical resection, which can result in significant morbidity.

Typically, poorly defined borders.

Conventional pattern

  • Most common pattern; present at least focally in almost all tumors
  • Long sweeping fascicles with elongated, slender, spindled cells of uniform appearance and pale cytoplasm set in a collagenous stroma
  • No nuclear hyperchromasia, minimal cytologic atypia and variable mitotic rate (typically low but may be focally increased)

Hypocellular / hyalinized pattern:

  • Second most common pattern
  • More hypocellular, prominent stromal hyalinization, compressed and thin-walled vessels

Staghorn vessel pattern:

  • ~20% of cases
  • Prominent, dilated, branching blood vessels

Myxoid pattern:

  • ~15% of cases
  • Myxoid stroma with less discrete fascicles; lacks the typical thin-walled blood vessels

Keloidal pattern:

  • ~15% of cases
  • Variably sized bands of keloidal collagen fibers throughout the tumor; fascicles are disrupted, and typical vascular pattern is lacking

Nodular fasciitis-like pattern:

  • ~10% of cases
  • Spindle to stellate cells in a loose tissue culture arrangement with variable amounts of stromal hemorrhage

Hypercellular pattern:

  • ~5% of cases
  • Resembles conventional pattern but with increased cellular density and frequently overlapping nuclei
  • Without cytologic atypia or nuclear hyperchromasia

Positive stains:

  • Variable positivity for SMA and MSA; rarely focal desmin
  • Beta catenin (70 - 98%; higher in mesenteric / FAP associated tumors)
  • Cyclin D1 (71 - 75%)
  • Calretinin (75%)
  • Sex hormones may show variable staining: ER (8%), PR (0 - 33%), AR (6 - 53%)
  • Vimentin (100%)
  • Cathepsin D (100%; limited utility due to positive staining in normal stromal cells and other soft tissue tumors)

Negative stains:

  • CD34, S100, cytokeratins
  • DOG1, c-kit
  • Ki67 (low, ~1 - 3%)  

References:

Bonvalot S, Ternès N, Fiore M, Bitsakou G, Colombo C, Honoré C, Marrari A, Le Cesne A, Perrone F, Dunant A, Gronchi A. Spontaneous regression of primary abdominal wall desmoid tumors: more common than previously thought. Ann Surg Oncol. 2013 Dec;20(13):4096-102. doi: 10.1245/s10434-013-3197-x. Epub 2013 Sep 20. PMID: 24052312.

Kasper B, Ströbel P, Hohenberger P. Desmoid tumors: clinical features and treatment options for advanced disease. Oncologist. 2011;16(5):682-93. doi: 10.1634/theoncologist.2010-0281. Epub 2011 Apr 8. PMID: 21478276; PMCID: PMC3228186.

Zreik RT, Fritchie KJ. Morphologic Spectrum of Desmoid-Type Fibromatosis. Am J Clin Pathol. 2016 Mar;145(3):332-40. doi: 10.1093/ajcp/aqv094. Epub 2016 Feb 13. PMID: 27124915.

Heim-Hall J, Yohe SL. Application of immunohistochemistry to soft tissue neoplasms. Arch Pathol Lab Med. 2008 Mar;132(3):476-89. doi: 10.5858/2008-132-476-AOITST. PMID: 18318588.

West RB, Corless CL, Chen X, Rubin BP, Subramanian S, Montgomery K, Zhu S, Ball CA, Nielsen TO, Patel R, Goldblum JR, Brown PO, Heinrich MC, van de Rijn M. The novel marker, DOG1, is expressed ubiquitously in gastrointestinal stromal tumors irrespective of KIT or PDGFRA mutation status. Am J Pathol. 2004 Jul;165(1):107-13. doi: 10.1016/S0002-9440(10)63279-8. PMID: 15215166; PMCID: PMC1618538.

Lucas DR, al-Abbadi M, Tabaczka P, Hamre MR, Weaver DW, Mott MJ. c-Kit expression in desmoid fibromatosis. Comparative immunohistochemical evaluation of two commercial antibodies. Am J Clin Pathol. 2003 Mar;119(3):339-45. doi: 10.1309/an4e2etcj4r6jjuy. PMID: 12645334.

Huss S, Nehles J, Binot E, Wardelmann E, Mittler J, Kleine MA, Künstlinger H, Hartmann W, Hohenberger P, Merkelbach-Bruse S, Buettner R, Schildhaus HU. β-catenin (CTNNB1) mutations and clinicopathological features of mesenteric desmoid-type fibromatosis. Histopathology. 2013 Jan;62(2):294-304. doi: 10.1111/j.1365-2559.2012.04355.x. Epub 2012 Sep 28. PMID: 23020601.

Lazar AJ, Tuvin D, Hajibashi S, Habeeb S, Bolshakov S, Mayordomo-Aranda E, Warneke CL, Lopez-Terrada D, Pollock RE, Lev D. Specific mutations in the beta-catenin gene (CTNNB1) correlate with local recurrence in sporadic desmoid tumors. Am J Pathol. 2008 Nov;173(5):1518-27. doi: 10.2353/ajpath.2008.080475. Epub 2008 Oct 2. PMID: 18832571; PMCID: PMC2570141.

Lazar AJ, Tuvin D, Hajibashi S, Habeeb S, Bolshakov S, Mayordomo-Aranda E, Warneke CL, Lopez-Terrada D, Pollock RE, Lev D. Specific mutations in the beta-catenin gene (CTNNB1) correlate with local recurrence in sporadic desmoid tumors. Am J Pathol. 2008 Nov;173(5):1518-27. doi: 10.2353/ajpath.2008.080475. Epub 2008 Oct 2. PMID: 18832571; PMCID: PMC2570141.

CASE IMAGES