The Abnormality Of Chromosome 8 And The Gene Mutations Of APC Gene And β-catenin Gene In Desmoid-type Fibromatosis

PurposeTo analyze the clinicopathologic features of desmoid-type fibromatosis, and to detect trisomy 8 and mutations of the APC gene and β-catenin gene in this tumor with a purpose of exploring the mechanism of the tumorigenesis and progression of this disease.Methods1. The clinical and histopathologic features of 96 cases of desmoid-type fibromatoses were analyzed.2. Beta-catenin, cyclinD1, c-myc and Ki-67 proteins were immunohistochemically detected in 69 cases using formalin-fixed, paraffin-embedded tissues. Using the same materials, apoptosis of the tumor cells was examinated by TUNEL testing. PCR, denaturing high performance liquid chromatography assay and direct sequencing were performed to detect abnormalities of the APC gene and β-catenin gene.3. Interphase FISH was employed to detect the abnormality of chromosome 8 on formalin-fixed, paraffin-embedded sections of 20 desmoid-type fibromatoses.4. The ultrastructural features of desmoid-type fibromatosis were also investigated by electronic transmission microscoping in 2 cases.Results1. There were 23 male patients and 76 female patients (male to female; 1:3.8), with a median age of 30.5 years (ranging from 8 to 86 years). A female predominance was noticed in the young patients (younger than 40s) compared with older ones (older than 40s). Extra-abdominal lesions comprised 44.8% of all desmoid-type fibromatoses, and abdominal wall lesions comprised 35.4%. The lesions of pelvisand mesentery comprised 10.4% and 9.4%, respectively. Among all desmoid-type fibromatoses, 14.6% were recurrent lesions and the recurrent intervals varied from 6 months to 72 months. Patients with recurrent lesions were significant younger than patients with primary lesions.2. Macroscopically, desmoid-type fibromatoses varied considerably in size from small nodule to bulky mass according to the different sites. They were typically located inside the muscle and attached to fascia. The lesions were firm and cutting with a gritty sensation. On cross section, the cut surface revealed a glistening white, coarsely whorled or trabeculated surface. Microscopically, the lesions were typically poorly circumscribed with infiltration into the surrounding soft tissues. All of the cases studied were characterized by proliferation of elongated, slender, spindle-shaped cells of uniform appearance, setting in a collagenous stroma containing variably prominent vessels. Ultrastructurally, most tumor cells showed fibroblastic differentiation and a subset of tumor cells had myofibroblastic features such as fibronexous junction, stress fiber, and intercellular junctions. Immunohistochemically, most cells reacted intensively to vimentin and were variably positive for smooth muscle actin and desmin.3. Six of 20 cases (30%) contained cell subpopulations with trisomy 8, 1 found in the 12 primary lesions, and the other 5 in the 8 recurrent lesions. The incidence of trisomy 8 in the recurrent lesions (62.5%, 5/8) was significant higher than that of primary lesions (8.3%, 1/12).4. Somatic mutations of APC gene and (or) β-catenin gene were detected in 40.6% of all the cases. APC mutations were found in 18 cases, and all these mutations were substitution and could not result in the expression of truncated APC protein. No mutation was detected in the 2 cases with familial adenomatous polyposis. Somatic mutations of β-catenin gene were detected in 13 (18.8%) and the mutations at codon 41 in exon 3 involved threonine resides implicated in the degradation of β-catenin.5. Beta-catenin protein was expressed abnormally in the cytoplasm and nucleus in 33 tumors, and no correlation of β-catenin expression with the mutations of APC gene or β-catenin gene was identified. Tumors with β-catenin gene mutations expressed cyclinDl proteins more frequently (69.2%, 9/13) compared to the tumors without such mutation (37.5%, 21/56). The cases with abnormal β-catenin protein expression showed a higher level of c-myc protein expression than thosewithout such abnormalities, although no significant difference of cyclinDl protein was observed.6. The Ki-67 indexes were extremely low in all the lesions. The lesions had low apoptosis index ranging from 0.01 to 0.05 with the mean of 0.022. The apoptosis indexes were significant lower in cyclinDl positive cases and c-myc positive cases. No significant influence of β-catenin protein on AI was found.Conclusions1. Desmoid-type fibromatosis is a clonal fibroblastic proliferative disease which arises in the deep soft tissues and is characterized by infiltrative growth and a tendency toward local recurrence but an inability to metastasize. Most are extra-abdominal lesions and a female predominance is noticed.2. The gross appearance of the lesions varies considerably in size according to the different sites. Microscopically, the lesions show longitudinally oriented fascicles of spindled fibroblasts and myofibroblasts in a prominently collagenous background. The ultrastructural hallmarks of myofibroblasts are fibronexous junction, stress fiber and intercellular junctions.3. Desmoid-type fibromatosis contains cell subpopulations with trisomy 8. Trisomy 8 serves as a useful predictor of recurrence.4. There are somatic mutations of the APC gene and β-catenin gene in the desmoid-type fibromatosis, and there are abnormalities in the Wnt signaling pathway. These abnormalities maybe result in the aberrances of cell proliferation and apoptosis, which are likely to be the import factors of the tumorigenesis and progression.5. There are probably two different groups of desmoid-type fibromatosis according to the abnormality of chromosome 8 and Wnt signaling pathway, so it probably has significant referenced meaning of practice in the clinical work when need choose different therapeutic methods.6. FISH testing can be used in archival formalin-fixed, paraffin-embedded tissues after successful pretreatment and optimization work and DHPLC is a sensitive and specific method to detect gene mutations.