The histologic response of soft tissue sarcoma to radiation therapy.

Twenty-seven patients with soft tissue sarcoma had preoperative radiotherapy, limb-sparing marginal surgical resection and whole-mount tumor histologic analysis. Incisional biopsy specimens before radiotherapy were reviewed for tumor type, grade, and extent of necrosis. Preoperative radiotherapy was given in either of two regimens: 13 patients received a mean total dose of 5250 cGy in one daily 180 to 200 cGy fractions and 14 patients a mean total dose of 4770 cGy in two daily fractions of 180 to 200 cGy separated by 4 hours. Twenty-one specimens had at least 80% necrosis or severely altered cells, a 3+ to 4+ response. Grade and size of the tumor appeared to be indicators of response to treatment rather than histologic type. Three of five patients (60%) with Grade 1, eight of 11 patients (73%) with Grade 2 lesions, and ten of 11 patients (91%) with Grade 3 tumors had 80% or greater necrosis or severely altered cells. For tumors 10 cm or less in greatest diameter, the 3+ to 4+ histologic response was seen in 12 of 14 patients (86%) whereas for lesions greater than 10 cm, this response was observed in nine of 13 patients (69%). For patients with Grade 2 or 3 soft tissue sarcoma, 13 of 14 patients (93%) treated with two fractions per day and two of four patients (50%) receiving one fraction per day exhibited significant response. All six patients treated twice daily for lesions greater than 10 cm had 3+ to 4+ histologic response compared to three of seven (43%) patients treated once per day. Therefore, grade and size of soft tissue sarcoma are important predictors of response to radiotherapy and preoperative twice daily radiotherapy may more likely permit the conservative surgical excision of sarcomas of borderline resectability.