This is a case report of a spontaneously regressed myxofibrosarcoma successfully treated by resection where the extent of the tumor was determined from the initial MRI. This case demonstrates that myxofibrosarcoma has the potential to regress spontaneously, and an astute awareness of this phenomenon is necessary for appropriate management of this condition.
A 62-year-old man was referred to our clinic with a gradually enlarging mass from one year ago in his right thigh. On physical examination, there was a 10 cm non-tender mass on his anterior thigh. The overlying skin was taut and adherent with slight hotness. On X-ray, there was no obvious calcification or scalloping of the femur. MRI revealed an elongated 8.6 × 13.3 × 1.9 cm bland mass which showed low intensity on T1WI and high intensity on T2WI with a tail like a sign in the subcutaneous tissue. Gadolinium administration showed uniform enhancement of the tumor without any peripheral inflammation or edema. The laboratory data including white blood cells, neutrophils, and C-reactive protein were all in the normal range. On positron emission tomography-computed tomography (PET – CT), there was no accumulation of 18F – FDG besides the thigh. Differential diagnosis included benign lesions such as nodular fasciitis and malignant tumors such as myxofibrosarcoma and undifferentiated pleomorphic sarcoma; therefore, an open biopsy was performed. On histological examination, the lesion was composed of spindle and pleomorphic tumor cells with atypical nuclei admixed with myxoid stroma. On immunohistochemistry, the lesion was positive for vimentin, CD34 and Ki67 (21.5%), suggestive of myxofibrosarcoma. During the preoperative period for wide resection, repeat MRI was performed to assess the extent of the hemorrhage 21 days after the open biopsy. Although the pattern of signal intensities was the same, there was a significant decrease in size from 8.6 × 13.3 × 1.9 to 6.0 × 8.5 × 0.9 cm. Since we didn’t perform any medical treatments other than open biopsy, we determined it to be a spontaneous regression of the tumor; however, due to the unpredictable nature of the phenomenon, wide resection with skin graft was performed. At the time of the surgery 34 days after the open biopsy, the tumor has regressed even further where it was difficult to palpate the mass. The margin of resection was determined from the MRI of the initial onset, 3 cm from the edge of the tumor. On gross examination, the resected specimen was tan white residing in the subcutaneous tissue measuring 3.7 × 2.5 × 1.2 cm. Histologically, over 95% of the residual lesion was composed of prominent fibrosis and granulation with myxomatous change by hematoxylin and eosin (HE) staining. There were abundant foamy cells, lymphocytes and plasma cell proliferation around small vessels, and sporadic atypical cells, most likely degenerated tumor cells, were present in a very small part of the lesion. Immunohistochemically, CD68, vimentin and Ki67 (5.4%) were positive. Based on these histological and radiographic findings, spontaneous regression of myxofibrosarcoma was chosen as the final diagnosis. The postoperative period was uneventful, and at the final follow-up after one year postoperatively, no local recurrence or metastasis has been observed.