undifferentiated pleomorphic sarcoma ( ups ) , formerly known as malignant fibrous histiocytoma ( mfh ) , is a common soft tissue sarcoma in which any attempt to describe the line of differentiation fails . ups was first described by ozzello et al . in 1963 , and feldman and norman first described primary malignant tumor of bone in 1972 ( quoted from ) . it most commonly involves the extremities and retro - peritoneum . in the head and neck region , the most commonly affected sites are the nasal cavity and the paranasal sinuses ( 54.3% ) . the mandible is a rare location , accounting for only 3% of tumors within bones . ups of head and neck that extend into bony structures are associated with a much more aggressive clinical course than those that are restricted to soft tissues . in this article , we report a rare case of ups of the mandible in a 44-year - old korean man . a 44-year - old man was referred to dankook dental hospital from a local neurosurgery clinic . the patient presented with the chief complaint of a rapidly growing mass in the left mandible area within the last two months . extra - oral examination revealed a tender , 4 to 5 cm sized solid mass in the left mandible area . no specific lesion such as ulcer or infection was found in intra - oral examination . the patient s medical history was non - contributory and there was no history of trauma or dental treatment recently . nothing remarkable was found through laboratory data including complete blood count , urine analysis , or chest x - ray in the preoperative exam . preoperative panoramic radiographs showed an ill - defined radiolucent , radiopaque mixed lesion on the left mandible area ( fig . 1 ) . a neck computed tomography ( ct ) with contrast revealed a 4 cm heterogeneously enhancing mass lesion in the left mandible body extending to adjacent soft tissue with bony destruction . 2 ) . positron emission tomography - computed tomography ( pet - ct ) revealed a large lobulating hypermetabolic lesion in and around the left submandibular area with possible bone invasion . in both lungs , a few tiny nodular opacities were seen , but these were too small to be characterized ( fig . 3 ) . with a clinical diagnosis of malignant tumor of the mandible , surgery was performed . under general anesthesia , a mandibulectomy from the symphysis to the left ascending ramus was performed , and reconstructed with vascularized osteocutaneous fibula free flap . to stabilize the flap , inter - maxillary fixation with arch - bar was applied in right half maxilla and mandible ( fig . the main tumor mass , with hematoxylin and eosin staining , was highly vascular and hypercellular with an apparent whitish slit - like hemorrhagic space at 100 magnification . at 200 magnification , tissue presented generalized myxoid pattern with a loose matrix . the tumor consisted of fibroblast - like spindle - shaped cells , specifically osteoclast - like giant cells with remarkably active mitosis . at high - power field ( 400 magnification ) , nuclear pleomorphism with prominent nuclei that varied in size , figure , and postoperatively , the patient was referred to the department of hemato - oncology for adjuvant chemotherapy . upon examination at two months , metastasis to the lung and local recurrence on primary mandible area was detected in pec - ct . thus , metastatectomy was performed for metastasis of lung , and the patient is receiving continuous palliative chemotherapy . the older term for ups was mfh , based on the resemblance of the cells to histiocytes and fibroblasts ( due to their elongated shapes ) . the name was modified to ups because the morphologic pattern of mfh is similar to many other sarcomas . the usual presentation in the literature is a painful mass that expands over a few weeks or months . in our case , the patient was a male in his forties , complaining of a rapidly growing painful mass . non - specific symptoms such as paresthesia make diagnosis of the tumor by clinical symptoms difficult . this implies that some of these tumors may represent an initial proliferative response to trauma . ups is either primary or secondary , and secondary tumors are more aggressive and less common than primary tumors . park et al . reported in a review that ct and magnetic resonance imaging ( mri ) features of ups of head and neck are nonspecific . on ct scans , ups appears as a non - specific , large , lobulated , soft tissue mass iso - attenuated to muscle . central areas of low attenuation may be due to necrosis , hemorrhage or myxoid material . in 5% to 20% of the cases , calcification or ossification can be detected . on mri , ups shows a heterogeneous hyper - intense pattern on t2-weighted images and isointensity that is almost same as muscles on t1-weighted images . non - immunoreactivity for pan - ck , ck8 , ck18 allows sarcomatoid or anaplastic hepatocellular carcinoma and cholangiocarcinoma to be ruled out . angiosarcomas are excluded due to no reactivity for the usual vascular antigens , such as cd31 , cd34 . liposarcoma or malignant peripheral nerve sheath tumor ( s-100 ) , rhabdomyosarcoma ( desmin ) , malignant melanoma ( s-100 and hmb-45 ) , malignant lymphoma ( lca ) are also excluded . s100 , desmin , s-100 , hmb-45 , lca in parenthesises are antibody of liposarcoma , rhabdomyosarcoma , malignant melanoma , malignant lymphoma respectively . fine needle aspiration biopsy can be used for obtaining of biopsy samples , but sensitivity is poor , ranging from 60% to 80% . this is due to the inability to obtain immunohistochemical stains on most samples from fine needle aspiration biopsy . the management of ups of the mandible requires early radical surgery including removal of adjacent normal tissue , with a minimum of 3 cm tumor - free margins . elective neck dissection is performed only when there is an evidence of cervical lymph node metastasis . the patient should be re - examined often to rapidly detect local recurrence and distant metastasis . the efficacy of chemotherapy and radiotherapy treatment for ups of mandible is not well established . this is based on randomized trials comparing surgery with or without radiotherapy that demonstrate the efficacy of radiotherapy as an adjuvant treatment in decreasing local recurrence rates . adjuvant radiotherapy may be indicated for patients with probable insufficient surgical margin when re - resection is not possible . one observer noted that cyvadic did not improve the prognosis , and a more intensive regimen could have been more effective . therefore , if adjuvant chemotherapy is needed , more intensive chemotherapy might be employed only for the high - risk group such as tumors with history of local recurrence and histologically high - grade because of possible subclinical or microscopic metastasis . perhaps 25% to 35% of patients with ups of head and neck region will develop metastases , with the lungs as the most common metastatic site from ups in the head and neck , followed by bone and liver . in this case , we detected no lymph node metastasis at the pre - operative examination so we did not perform neck dissection . this infiltrative growth is an adverse prognostic factor not only for local control , but also for disease - free and meta - stasis - free survival . tumor infiltration into adjacent soft tissue including muscles occurred in this case , accompanied by local recurrence . background ( primary or recurrent ) , histologic grade , tumor size , and surgical margin are the significant prognostic factors for the outcome after surgical treatment . in conclusion , the diagnosis of ups should be reserved only for those cases in which any attempt to identify a line of differentiation has failed . due to the low numbers of patient with ups of the head and neck region , a consistent therapeutic strategy for this disease is unlikely to be established .