A pimarane diterpenoid, having the following structure: or a tautomer thereof in which R1 and R2 are independently selected from —H, C1-10 alkyl, C1-10 alkoxy, C1-10 alkenyl, C1-10 alkenoxy, —OH, —OAc, —CHO, -Ph, —OC6H5, —OC6H4OH, —COC6H5, —OCONH2, —OCONHCH3, —OCOC6H4NH2, —NH2, or ═O based on an isolate from the plant Hymenocrater elegans is utilized in the prevention of growth and development of pathogenic cells, e.g., cancer cells. The compound shows efficacy in treatment and prevention of a wide range of cancer types as well as other neoplastic diseases as a chemo-preventative, a primary or secondary cytotoxic agent, a sensitizer for other therapies, or one component of a combinatorial treatment.