1. The treatment of disease, especially of parasitic infections or cancer, by means of chemical substances which act selectively on micro-organisms or malignant tissue.
2. Treatment of disease by means of chemical substances or drugs; usually used in reference to neoplastic disease (a new and abnormal formation of tissue; such as, a tumor or other growth). Also known as, pharmacotherapy.
3. The treatment of a disease with chemicals or drugs; used especially in reference to the treatment of cancer with chemicals.