Threshold is presently testing TH-302 along with a commonly used chemotherapeutic agent, doxorubicin, in a late-stage trial to treat soft tissue sarcoma.
The orphan status can provide a seven-year marketing exclusivity for the drug from the date of approval.
The experimental drug had received orphan status from European health regulators.
Threshold chief executive Barry Selick said: "The results of our Phase 2 study (TH-CR-403) in soft tissue sarcoma are certainly supportive of a pivotal trial underway in this difficult to treat cancer."