The extension, which was granted through the Hatch-Waxman Act, postpones the original 16 July 2017 expiration date to 16 July 2022.
Spectrum Pharmaceuticals chairman, president and chief executive officer Rajesh Shrotriya said the drug is an important treatment option in relapsed or refractory PTCL.
"In addition, the patent extension confirms substantial expected revenue growth for the Company in the near- and long-term," Shrotriya added.
Folotyn, a folate analogue metabolic inhibitor, was indicated for use as a single agent for the treatment of patients with relapsed or refractory PTCL.