Wnt targets genes are not differentially expressed in desmoid tumors bearing different activating ß-catenin mutations.

INTRODUCTION: Sporadic desmoid-type fibromatosis (DTF) is a rare soft tissue tumor of mesenchymal origin. It is characterized by local invasive growth and unpredictable growth behavior. Three distinct mutations involving the CTNNB1 (ß-catenin) gene have been identified in the vast majority of DTF tumors, which cause activation of the Wnt signaling pathway and impact prognosis. This study examines whether the different CTNNB1 mutants (T41A, S45F) occurring in DTF tumors differentially affect Wnt signaling activity, which might explain the different disease course between DTF patients harboring different CTNNB1 mutations. MATERIALS AND METHODS: Real-time polymerase chain reaction (RT-PCR) on 61 formalin fixed paraffin embedded DTF samples with known CTNNB1 status was used to measure the relative mRNA expression level of Wnt target genes AXIN2, DKK1 and CCND1. Additionally, publicly available mRNA expression data retrieved from the Gene Expression Omnibus of 128 DTF samples were used for an unsupervised cluster analyses based on the expression of a selection of Wnt targets. RESULTS: No statistically significant difference in relative expression levels of Wnt target genes AXIN2, DKK1 and CCND1 was identified between either CTNNB1 wild-type, S45F or T41A mutated DTF samples. Moreover, the hierarchical cluster analyses using selected Wnt targets did not discriminate between different CTNNB1 mutation types. CONCLUSIONS: No differences in the expression levels of Wnt target genes were observed between the different CTNNB1 mutation types in DTF tumors. Further studies are needed to decipher the mechanism accounting for the diverse disease courses between DTF patients with different CTNNB1 variants.

APC mosaicism in a young woman with desmoid type fibromatosis and familial adenomatous polyposis.

Familial adenomatous polyposis (FAP) is usually caused by germline mutations in the adenomatous polyposis coli (APC) gene. The classic form is characterized by hundreds to thousands of adenomas in the colorectum and early onset colorectal cancer (CRC) if left untreated. FAP is also associated with multiple extra-colonic manifestations such as gastroduodenal polyps, osteomas, epidermoid cysts, fibromas and desmoids. Most desmoid tumours in FAP patients occur intra-abdominally. Approximately 15-20% of the APC mutations are de novo mutations. Somatic mosaicism has been reported in some sporadic cases of polyposis but is probably an underestimated cause of the disease. This case report presents the detection of a mosaic APC mutation in a 26-year-old woman who as a child had been diagnosed with desmoid type fibromatosis. FAP was suggested when she presented with extensive extra abdominal fibromatosis. Our findings indicate that APC mutations may be suspected in patients presenting with a desmoid regardless of its location. If there is clinical evidence that the patient has FAP, adenomas and colonic mucosa in addition to leukocyte DNA should be included in the screening, preferably using methods that are more sensitive than Sanger sequencing.

A Patient With Desmoid Tumors and Familial FAP Having Frame Shift Mutation of the APC Gene.

Desmoids tumors, characterized by monoclonal proliferation of myofibroblasts, could occur in 5-10% of patients with familial adenomatous polyposis (FAP) as an extra-colonic manifestation of the disease. FAP can develop when there is a germ-line mutation in the adenomatous polyposis coli gene. Although mild or attenuated FAP may follow mutations in 5΄ extreme of the gene, it is more likely that 3΄ extreme mutations haveamore severe manifestation of thedisease. A 28-year-old woman was admitted to the Cancer Institute of Iran with an abdominal painful mass. She had strong family history of FAP and underwent prophylactic total colectomy. Pre-operative CT scans revealed a large mass. Microscopic observation showed diffuse fibroblast cell infiltration of the adjacent tissue structures. Peripheral blood DNA extraction followed by adenomatous polyposis coli gene exon by exon sequencing was performed to investigate the mutation in adenomatous polyposis coli gene. Analysis of DNA sequencing demonstrated a mutation of 4 bpdeletions at codon 1309-1310 of the exon 16 of adenomatous polyposis coli gene sequence which was repeated in 3 members of the family. Some of them had desmoid tumor without classical FAP history. Even when there is no familial history of adenomatous polyposis, the adenomatous polyposis coli gene mutation should be investigated in cases of familial desmoids tumors for a suitable prevention. The 3΄ extreme of the adenomatous polyposis coli gene is still the best likely location in such families.

Sporadic desmoid tumors of the abdominal wall: the results of surgery.

PURPOSE: Before the wait-and-see policy became the standard approach in abdominal wall desmoid tumors, surgery was performed on a systematic basis. Surgery remains indicated for progressing tumors but its extent is debatable. The abdominal wall is a common site of origin of sporadic desmoids, usually associated with a favorable prognosis. We analyzed the results of surgery at this specific site. METHODS: Data from 33 patients affected by sporadic desmoid tumors of the abdominal wall (31 primary, 2 recurrent) consecutively treated at our cancer center between January 2000 and September 2013 were retrospectively studied. RESULTS: Twenty-nine patients underwent surgery upfront and 1 after progression during the initial wait-and-see period. Prosthetic reconstruction of the abdominal wall was required in 28 patients. The average hospital stay was 5 days. Three patients developed surgical complications. Local recurrence-free survival was 90% at 5 and 10 years. Three patients had an uneventful childbirth during the follow-up after surgery. CONCLUSIONS: Desmoid tumors of the abdominal wall have a favorable prognosis after surgical resection, which remains a safe and effective treatment. Wild-type tumors are common, whereas the incidence of S45F mutation in the beta-catenin gene is lower than in other anatomic sites. Upfront surgery may be considered in selected women who wish to bear a child.

Low-dose chemotherapy with methotrexate and vinblastine for patients with desmoid tumors: relationship to CTNNB1 mutation status.

BACKGROUND: This study was conducted to determine the efficacy and safety of low-dose chemotherapy with methotrexate (MTX) and vinblastine (VBL) for patients with desmoid tumors refractory to meloxicam treatment, focusing in particular on the relationship between the efficacy of this chemotherapy and catenin ß-1 (CTNNB1) mutation status. PATIENTS AND METHODS: Since March 2003, patients pathologically diagnosed with extraperitoneal desmoid tumors have been prospectively treated with meloxicam, a COX-2 inhibitor, at our institution. Patients with inoperable tumors who were resistant to meloxicam treatment underwent MTX and VBL therapy every other week. The responses of all patients were evaluated, and factors that were correlated with efficacy were analyzed, including CTNNB1 mutation status. RESULTS: Sixty-eight patients were prospectively treated with meloxicam. MTX + VBL therapy was administered in 15 patients. Six patients showed a partial response. Only one patient presented disease progression. A few patients showed grade 3-4 treatment-related toxicity with the administration of MTX and VBL every other week. Intriguingly, CTNNB1 status did not affect the efficacy of this treatment. CONCLUSION: MTX and VBL treatment every other week is well tolerated and achieved a favorable response in patients resistant to meloxicam treatment, regardless of CTNNB1 mutation status.

CTNNB1 S45F mutation predicts poor efficacy of meloxicam treatment for desmoid tumors: a pilot study.

We hypothesized that patterns of CTNNB1 (ß-catenin) mutations would affect the outcome of conservative therapy in patients with desmoid tumors. This study aimed to determine the significance of CTNNB1 (ß-catenin) mutations in predicting the treatment outcome in patients with desmoid tumors treated with meloxicam, a cyclooxygenase-2 (COX-2) selective inhibitor. Between 2003 and 2012, consecutive thirty-three patients with extra-peritoneal sporadic desmoid tumors were prospectively treated with meloxicam as the initial systemic medical therapy. The efficacy of meloxicam was evaluated according to Response Evaluation Criteria in Solid Tumors (RECIST). DNA was isolated from frozen tissue or formalin-fixed materials. CTNNB1 mutation analysis was performed by direct sequencing. Positivity of nuclear ß-catenin staining by immunohistochemistry was compared with the status of CTNNB1 mutations. The correlation between the efficacy of meloxicam treatment and status of CTNNB1 mutations was analyzed. Of the 33 patients with meloxicam treatment, one showed complete remission (CR), 7 partial remission (PR), 12 stable disease (SD), and 13 progressive disease (PD). The following 3 point mutations were identified in 21 of the 33 cases (64%): T41A (16 cases), S45F (4 cases) and S45P (one case). The nuclear expression of ß-catenin correlated significantly with CTNNB1 mutation status (p = 0.035); all four cases with S45F mutation exhibited strong nuclear expression of ß-catenin. S45F mutation was significantly associated with a poor response (all cases; PD) (p = 0.017), whereas the other mutations had no impact on efficacy. The CTNNB1 mutation status was of significant prognostic value for meloxicam treatment in patients with sporadic desmoid tumors.

CTNNB1 mutation analysis is a useful tool for the diagnosis of desmoid tumors: a study of 260 desmoid tumors and 191 potential morphologic mimics.

Desmoid tumors are benign monoclonal fibroblastic or myofibroblastic neoplasms, characterized by local invasiveness and high rates of recurrence. Desmoid tumors must be distinguished from benign fibroblastic and myofibroblastic lesions, as well as from low-grade sarcoma, which can appear histologically similar to desmoid tumors. This differential diagnosis can be very difficult, especially when diagnosis is based on a core needle biopsy. On the molecular level, most sporadic desmoid tumors are associated with mutations of the ß-catenin gene (CTNNB1). A minority of desmoid tumors are associated with Gardner syndrome and mutations of the familial adenomatous polyposis gene. We identified the common CTNNB1 mutations associated with sporadic desmoid tumors by direct sequencing: in (i) 260 cases of typical desmoid tumors; and (ii) in 191 cases of spindle cell lesions, which can morphologically 'mimic' desmoid tumors. Formalin-fixed paraffin-embedded tissues were obtained via core needle biopsy (n=150) or open biopsy/surgical excision (n=301). Only 16 cases (4%) were not analyzable (Bouin's fixed tissue). CTNNB1 mutations were observed in 223 of 254 (88%) of sporadic desmoid tumors. No CTNNB1 mutations were detected in all other lesions (n=175) studied. CTNNB1 sequencing can be easily and reliably done using tissues obtained via core needle biopsy. Detection of CTNNB1 mutations in formalin-fixed paraffin-embedded tissues among spindle cell lesions is proposed as a specific diagnostic tool for the diagnosis of desmoid tumors. This result has significant implications for patient care and management.

Immunohistochemical characteristics of desmoid tumors.

A comparative morphological study of primary and relapsing desmoid tumors was carried out. Immunohistochemical analysis showed that the progress of desmoid tumors in the form of relapses was paralleled by an increase in the counts of immunopositive cells and intensity of ß-catenin and cycloxygenase-2 expression.

Family history, surgery, and APC mutation are risk factors for desmoid tumors in familial adenomatous polyposis: an international cohort study.

BACKGROUND: Ability to identify patients with familial adenomatous polyposis who have a high risk of developing desmoid tumors may affect decisions in clinical practice. OBJECTIVES: Our aim was to assess several risk factors for desmoid tumor development in an international cohort of patients with familial adenomatous polyposis and to evaluate the clinical relevance of risk factors. DESIGN: This was a retrospective cohort study. SETTING AND PATIENTS: Polyposis registries in The Netherlands, France, Denmark, Finland, and Italy provided information on familial adenomatous polyposis patients with desmoid tumors. MAIN OUTCOME MEASURES: We used univariate and multivariable analyses of data from registries in The Netherlands, France, Denmark, and Finland to test whether gender, APC mutation site, previous colorectal surgery, colorectal cancer, and family history for desmoid tumors contribute to risk of developing desmoid tumors at any location, or specifically at an intra-abdominal location. The effect of family history was tested with a generalized linear mixed model. RESULTS: : Of 2260 patients with familial adenomatous polyposis from 912 families in The Netherlands, France, Denmark, and Finland, 220 patients (10%) had desmoid tumors (101 men). In 387 patients with desmoid tumors (including 167 patients from the Italian registry), the median age at diagnosis of the first desmoid tumor was 31 years (range, 4 months-74 years). Desmoid locations were intra-abdominal (53%), abdominal wall (24%), extremities (9%), and unknown sites or combinations of sites (14%). Multivariable analysis of risk factors for desmoids at any location showed surgery (OR, 2.58; P = .0004), an APC mutation 3' of codon 1444 (OR, 3.0; P < .0001), and a positive family history (P < .0001) to be independently associated with desmoid development. When only intra-abdominal location was analyzed, APC mutation site was not associated with desmoid development. LIMITATIONS: Selection bias may have occurred. CONCLUSIONS: A positive family history for desmoid tumors, abdominal surgery, and APC mutation site are significant risk factors for development of desmoid tumors. The results may have implications for determining the optimal management of FAP patients and guide future studies.

'Difficult to diagnose' desmoid tumours: a potential role for CTNNB1 mutational analysis.

AIMS: The utility of CTNNB1 (encoding ß-catenin) genotyping for diagnosing sporadic desmoid tumours (DT) when traditional clinicopathological parameters were inconclusive was evaluated. METHODS AND RESULTS: Cases included were: (i) new primary lesions where initial DT diagnosis was inconclusive; and (ii) possible recurrent DT versus scar. Formalin-fixed paraffin-embedded (FFPE) tissues were obtained via needle biopsy or a surgical excision (57 specimens) as part of initial assessment. DNA extraction, CTNNB1 exon 3 amplification and sequencing were conducted in a Clinical Laboratory Improvement Amendments of 1988 (CLIA)-approved molecular diagnostics laboratory. For patients with no previous DT history (n = 47) sequencing identified mutations in 30 (64%), substantiating DT diagnosis. In biopsies with non-mutated (NM) CTNNB1 (n = 17) the test was inconclusive; in seven of these, a diagnosis of DT was strongly favoured in the subsequent surgical resection specimen. Ten patients with previously resected DT were evaluated; mutation was identified in six cases (60%), indicating DT over scar. In two (20%) with primary tumours harbouring CTNNB1 mutation no mutation was found, favouring scar over DT; the other two NM-CTNNB1 cases (20%) were inconclusive. CONCLUSIONS: CTNNB1 genotyping can be very useful in 'difficult to diagnose' lesions when the differential diagnosis includes DT. Recognizing inherent test limitations, the presence of CTNNB1 mutation can inform the therapeutic approach.

A 30 year old female with lower abdominal lump.

A female of 30 years of age, hailing from Narayangonj, Dhaka got admitted herself into Dhaka medical College & Hospital on 25.10.08 with the complaints of a lump in the lower abdomen for 1 year and pain in the lower abdomen for the same duration. Local examination reveals a lump in the lower abdomen which is intra abdominal, 10cm × 12cm in size. CT scan of Abdomen reveals a solid mass measuring (12 × 9 × 8.5) cm is seen in left side of abdominal cavity extending up to pelvic cavity. FNAC of abdominal lump shows sheets of mesothelial cells and few small clusters of regular epithelial like cells. Laparotomy was done on 27.11.08 under G/A & reveals a solid mass measuring about 10 × 8cm size & was well encapsulated, adherent with omentum found in the lower abdomen. Few mesenteric lymph nodes were enlarged. The mass was gently separated from the omentum ensuring adequate haemostasis. Post-operative period was uneventful. Histopathology report shows neoplasm composed of plump of fibroblasts arranged in broad sweeping fascicles and infiltrate into adjacent tissue consistent with fibromatosis. The patient was discharged with advice on 10th post operative day.

Risk factors for development of desmoid tumours in familial adenomatous polyposis.

BACKGROUND: Desmoid tumours (DTs) are the primary cause of death of patients with familial adenomatous polyposis (FAP) following restorative proctocolectomy. The aim of this study was to identify risk factors for DT in a French population. METHODS: Clinical data for 442 patients with FAP from 1983 to 2004 were reviewed retrospectively. RESULTS: A total of 124 DTs were documented in 50 patients (25 female). DT sites were mesenteric (73 tumours), abdominal wall (44) and extra-abdominal (seven). Female patients developed DT earlier than males. Although DTs appeared after colectomy in 34 patients, the type of surgery did not influence the risk of DT. An identified point mutation in the adenomatous polyposis coli (APC) gene after codon 1444 was a significant risk factor (hazard ratio 3.3 (95 per cent confidence interval 1.5 to 7.3)). Belonging to a family affected by DT did not increase the individual's risk in this population. CONCLUSION: No risk factor for life-threatening mesenteric DT could meaningfully modify the management of patients with FAP.

Mesenteric desmoid tumors in Singapore familial adenomatous polyposis patients: clinical course and genetic profile in a predominantly Chinese population.

PURPOSE: This study examined the mutational profile of the adenomatous polyposis coli gene in relation to the development of desmoid tumors in familial adenomatous polyposis patients from a predominantly Chinese population. METHODS: This is a retrospective review of all patients with familial adenomatous polyposis coli from the Singapore Polyposis Registry. Identification of specific adenomatous polyposis coli gene mutation was performed and clinical course of associated desmoid disease obtained from case records and a computerized database. RESULTS: Two hundred five patients from 75 families afflicted with familial adenomatous polyposis coli were reviewed, with gene mutations identified in 107 patients. Of these, 23 (11.2 percent) developed desmoids. The male-to-female ratio was 1:1.3 and the ethnic distribution was Chinese (n=17) and Malay (n=6). Of the 92 patients with mutations 5' to codon 1444, 11 patients (12 percent) developed desmoids compared with 6 of 15 (40 percent) patients with adenomatous polyposis coli gene mutations 3' to codon 1444 (P<0.01). The clinical course of desmoid tumors can be divided into stable (n=11), variable (n=3), progressive (n=6), and aggressive growth (n=3). Only 3 (13 percent) patients with aggressive tumor growth required chemotherapy. There was no correlation between the site of mutation and the clinical progression of the desmoids. Seventy-four percent of these desmoids (17/23) developed at a mean interval of 2.98 years after restorative proctocolectomy, while only 30 percent (7/23) were diagnosed preoperatively or discovered during the initial surgery. The most common complications related to the mesenteric desmoids were intestinal obstruction (21.7 percent), ureteric obstruction (17.4 percent), and encasement of superior mesenteric vessels (13 percent). CONCLUSION: The clinical course of desmoids in an individual familial adenomatous polyposis patient remains unpredictable and no reliable genetic marker is available for prognostication in desmoid disease.

Immunohistochemical and mutational analysis of PDGF and PDGFR in desmoid tumours: is there a role for tyrosine kinase inhibitors in c-kit-negative desmoid tumours?

AIM: To determine the platelet-derived growth factor (PDGF) alpha and beta status of desmoid tumours. Desmoid tumours are rare monoclonal neoplasms that appear to have no metastatic potential. Surgical resection and radiotherapy in the event of a positive surgical margin is the first-line treatment. Recurrences are frequent. Treatment results using non-steroidal anti-inflammatory agents, anti-oestrogen compounds and other agents such as Imatinib mesylate have been published. Therapy with Imatinib has been proposed as a therapeutic option, although in most reports desmoid tumours are reported to be c-kit-. METHODS AND RESULTS: We performed immunohistochemical analysis on 124 archived samples (85 patients) of desmoid tumours using antibodies to PDGFalpha, PDGFbeta, PDGFRalpha and PDGFRbeta. All desmoid tumours showed immunoreactivity with antibodies to PDGFalpha and PDGFRalpha, whereas with antibodies to PDGFbeta and PDGFRbeta no specific reaction could be detected. Mutational analysis of PDGFRalpha (exons 11, 12, 17 and 18) and PDGFRbeta (exon 12) on frozen material from 14 patients was performed, but no mutations leading to amino acid changes in the mature protein were identified. CONCLUSION: The absence of an activating mutation in a protooncogene does not exclude the efficacy of tyrosine kinase inhibitors through other possible mechanisms, and these might be a therapeutic option for patients with desmoid tumours in whom established local and systemic approaches fail to control the disease.

[Clinicopathologic and genetic studies of desmoid-type fibromatosis].

OBJECTIVE: To study the clinicopathological and genetic features of desmoid-type fibromatosis, and to investigate the feasibility of detecting trisomy 8 in formalin fixed, paraffin embedded (FFPE) tissue by fluorescence in-situ hybridization (FISH). METHODS: A total of 96 cases were included in this study. All patients had clinical information. Histopathologic and immunohistochemical evaluations were available in 69 cases, and ultrastructural evaluation was done in 2 cases of desmoid-type fibromatosis. FFPE tissue sections were available in 20 tumors for the trisomy 8 detection by FISH. RESULTS: There were 20 male and 76 female patients with ages ranging from 8 to 86 years (mean 35.3 years). Clinically, there were 44 extra-abdominal tumors, 28 abdominal wall tumors and 23 intra-abdominal lesions mostly involving the mesentery. Most cases presented with nodular or funicular masses with white firm cut surfaces, measuring 0.6 to 24.0 cm (mean 8.4 cm) in size. Histologically, desmoid-type fibromatoses showed longitudinal fascicles of spindle fibroblasts and myofibroblasts in a predominantly collagenous background. The tumor cells stained positive for vimentin, alpha-smooth muscle actin, desmin, and beta-catenin (47.8%, 33/69). Ultrastructurally, most tumor cells had features of fibroblasts, including rich endoplasmic reticulum and Golgi apparatus. Some tumor cells were myofibroblast-like cells exhibiting intercellular junctions, fibronexous junctions and stress fibers. Trisomy 8 was detected in 6 of 20 cases of desmoid-type fibromatosis including 5 of the 8 recurrent tumors but only one of the 12 primary tumors. The latter tumor also recurred three years later. CONCLUSIONS: Desmoid-type fibromatosis is an intermediate (locally aggressive) tumor that occurs predominantly in young females. The lesion consists of fibroblasts and myofibroblasts with the latter showing characteristic features including stress fibers and fibronexous junctions. Trisomy 8 can be detected in FFPE tissue by FISH, and its presence serves as a useful predictor of tumor recurrence and may define a subtype of desmoid-type fibromatosis with high recurrence rate.

Analysis of p27KIP1 protein and Ki-67 expression in aggressive fibromatosis (desmoid tumor).

Aggressive fibromatosis (desmoid tumor) is an uncommon locally invasive non-metastasizing neoplasm lesion. Desmoid tumor consists of fibroblasts, miofibroblasts and a significant amount of extracellular matrix. p27KIP1 (p27) protein is a member of the universal cyclin-dependent kinase inhibitor (CDKI) family that regulates progression through the cell cycle. In various human neoplasms the decreased level of p27 was observed. There were analysed 42 specimens of aggressive fibromatosis, in which there were 24 abdominal and 18 extra-abdominal cases. There was performed immunohistochemical analysis employing a monoclonal antibody against p27 protein and Ki-67 (Novocastra, UK). The sections for immunohistochemical study were stained using the streptavidin - biotin method. The average percentage of cells stained positively for all cases for p27 and Ki-67 was 22.1% (SD=29.2) and 6.0% (SD=8.8) respectively. There was no statistically significant difference between Ki-67 or p27 expression in abdominal and extra-abdominal location. Analysis of p27 and Ki-67 expression levels might indicate that low proliferating activity of desmoid fibroblasts is connected with another mechanism than the one, in which p27 takes part.

Familial polyposis coli: clinical manifestations, evaluation, management and treatment.

Familial adenomatous polyposis (FAP) is an autosomal dominant, hereditary colon cancer syndrome that is characterized by the presence of innumerable adenomatous polyps in the colon and rectum. Gardner's syndrome is a variant of FAP, which in addition to the colonic polyps, also presents extracolonic manifestations, including desmoid tumors, osteomas, epidermoid cysts, various soft tissue tumors, and a predisposition to thyroid and periampullary cancers. Mutations of the APC gene are thought to be responsible for the development of FAP, and the location of the mutation on the gene is thought to influence the nature of the extracolonic manifestations that a given patient might develop. Though patients are often asymptomatic, bleeding, diarrhea, abdominal pain and mucous discharge frequently occur. Diagnostic tools include genetic testing, endoscopy, and monitoring for extra-intestinal manifestations. Currently, surgery is the only effective means of preventing progression to colorectal carcinoma. Restorative proctocolectomy with ileal pouch anal anastomosis (RPC/IPAA) with mucosectomy is the preferred surgical procedure, since it attempts to eliminate all colorectal mucosa without the need for an ostomy. Periampullary carcinoma and intra-abdominal desmoid tumors are a significant cause of morbidity and mortality in these patients after colectomy. Frequent endoscopy is needed to prevent the former, while there is no definitive treatment available yet for the latter. The following article presents a case and reviews the evaluation, management and treatment of Gardner's syndrome.

Evidence for genetic predisposition to desmoid tumours in familial adenomatous polyposis independent of the germline APC mutation.

BACKGROUND: Many patients with familial adenomatous polyposis (FAP) die from desmoid tumours which can arise spontaneously but often appear to be surgically induced by prophylactic colectomy. FAP results from germline adenomatous polyposis coli (APC) gene mutations and desmoids arise following biallelic APC mutation, with one change usually occurring distal to the second beta-catenin binding/degradation repeat of the gene (3' to codon 1399). We have suggested that because families with germline mutations in this region already have the requisite change, they are more likely to develop desmoids. However, there are families with 5' germline mutations where desmoids are common. PATIENTS AND METHODS: We examined desmoid risk dependent on germline APC mutation, sex, history of abdominal surgery, and family history in FAP patients from the St Mark's Hospital Polyposis Registry. RESULTS: Overall desmoid prevalence was 15%. Desmoids tended to cluster in susceptible individuals, irrespective of the germline APC mutation. Independent predictors of increased desmoid risk were: germline mutation distal to codon 1399; any family history of disease; and a strong family history of desmoids. A family history of multiple desmoids (>1) increased an individual's own risk of multiplicity. Females had twice the odds of developing desmoids compared with males. There was no significant interaction between any of the three explanatory variables. CONCLUSIONS: Our results indicate the influence of unknown genetic factors independent of APC in susceptibility to desmoid tumours in FAP. The data have implications in terms of clinical management of FAP patients and assessing the balance between chemoprevention and prophylactic colectomy.