Myxofibrosarcoma is a malignant mesenchymal tumor and a fibroblastic sarcoma of the elderly. Myxofibrosarcoma can be low-grade or high-grade depending on the cell characteristics. Wide surgical resection with or without radiotherapy and chemotherapy is the basis of its treatment. Sometimes, tumor cells secrete insulin or insulin-like substances and cause hypoglycemia attacks. Here, we intend to demonstrate the role of early surgery to end hypoglycemia attacks and prevent recurrence and metastases. We also intend to show the insufficiency of tru-cut biopsy to distinguish between low- and high-grade myxofibrosarcoma. An 82-year-old male patient visited our clinic with a rapidly growing giant mass in the left retroscapular area and suffered from hypoglycemic attacks several times a day. After imaging and initial biopsy, the tumor grade was indeterminate on histopathological examination; hence, the mass was removed surgically. The pathological examination resulted in high-grade myxofibrosarcoma whereas the initial biopsy could not elaborate on the grade. The hypoglycemia attacks ceased after the surgery. Adjuvant local radiotherapy at a total dose of 60 Gy was administered in 30 fractions to the surgery area with no complications after the surgery. No new mass, recurrence, or hypoglycemia attack was detected in the three-year follow-up. In conclusion, hypoglycemia attacks may be a marker of malignant tumor presence and may be a clue at the beginning and in the follow-up period both for recurrence and the aggressiveness of the tumoral mass. Because a biopsy may show the diagnosis but not the grade of the tumor, early surgical intervention is needed.