Isatis leaf has not been shown to treat or prevent cancer.
Isatis leaf extract is derived from the same plant from which indigo dye is made. It is used in combination with isatis root and other herbs both in traditional Chinese medicine (TCM) and in Ayurveda to treat the common cold, sore throat, mumps, respiratory ailments, other febrile diseases, hepatitis, and malignant tumors. Isatis roothas both similar and different properties from isatis leaf.
Isatis leaf has anti-inflammatory properties. Lab studies suggest that indirubin, an active compound in isatis, stops cell duplication and therefore may be useful in cancer treatment, but studies in humans are lacking. Other lab experiments show that isatis extract can kill certain viruses and counteract some symptoms and tissue damage from bacterial infections.
Studies in humans are limited. Although it may be effective against ulcerative colitis, its use has been associated with a serious condition called pulmonary arterial hypertension. Therefore it should not be used outside of clinical trials. Additional studies are needed to determine safety and effectiveness.