Temozolomide regresses a doxorubicin‐resistant undifferentiated spindle‐cell sarcoma patient‐derived orthotopic xenograft (PDOX): precision‐oncology nude‐mouse model matching the patient with effective therapy

Undifferentiated spindle-cell sarcoma (USCS) is a recalcitrant cancer, resistant to conventional chemotherapy. A patient with high-grade USCS from a striated muscle was implanted orthotopically in the right biceps femoris muscle of mice to establish a patient-derived orthotopic xenograft (PDOX) model. The PDOX models were randomized into the following groups when tumor volume reached 100 mm3 : G1, control without treatment; G2, doxorubicin (DOX) (3 mg/kg, intraperitoneal [i.p.] injection, weekly, for 2 weeks); G3, temozolomide (TEM) (25 mg/kg, p.o., daily, for 14 days). Tumor size and body weight were measured with calipers and a digital balance twice a week. TEM significantly inhibited tumor volume growth compared to the untreated control and the DOX-treated group on day 14 after treatment initiation: control (G1): 343 ± 78 mm3 ; DOX (G2): 308 ± 31 mm3 , P = 0.272; TEM (G3): 85 ± 21 mm3 , P < 0.0001. TEM significantly regressed the tumor volume compared to day 0 (P = 0.019). There were no animal deaths in any group. The body weight of treated mice was not significantly different in any group. Tumors treated with DOX were comprised of spindle-shaped viable cells without apparent necrosis or inflammatory changes. In contrast, tumors treated with TEM showed extensive tumor necrosis. The present study demonstrates the potential power of matching the patient with an effective drug and saving the patient needless toxicity from ineffective drugs.