The hydrochloride form of eflornithine, a difluoromethylated ornithine compound with antineoplastic activity. Eflornithine irreversibly inhibits ornithine decarboxylase, an enzyme required for polyamine biosynthesis, thereby inhibiting the formation and proliferation of tumor cells. Polyamines are involved in nucleosome oligomerization and DNA conformation, creating a chromatin environment that stimulates neoplastic transformation of cells. (NCI04)