The authors have investigated the clinical usefulness of an in vitro chemo-sensitivity assay for soft tissue sarcoma using tumor xenografts. Biopsy or surgical specimens from 47 patients with soft tissue sarcoma were trans-planted into nude mice. In vitro chemosensitivity of each patient was deter-mined using these early-generation xenografts by means of in vitro scintilla-tion assay. Thirty-three of 47 clinical samples (70.2 %) obtained from patients were successfully transplanted into nude mice. Of these 33 xeno-grafts, 25 met the criterion for in vitro growth. Overall, 25 of 47 (53 %) samples gave a successful assay. Twenty-four of the 47 patients died of metastatic disease at a median of 26.3 months (range, 2 to 86 months) . Five patients were excluded from this study: one patient died of chemotherapy side effects, one died of lung cancer and the other three were dropped out. The average follow-up period of 18 surviving patients was 85 months (range, 60 to 116 months) . A significant difference in the five-year survival rate was noted between the patients with a successful assay (36.6 %) and those with a failed assay (56.1 %) . Retrospectively, the in vitro results were compared with the clinical responses of 16 patients who received systemic chemotherapy and operation. The true positive rate, true negative rate, and predictive accuracy were 33 %, 100 %, and 75 %, respectively. The authors suggest that this in vitro chemosensitivity assay system provides a valid tool for prognosis and facilitates the exclusion of ineffective drugs for treating cases of soft tissuesarcoma. As a result, a more efficient therapy for this disease may be obtained
