[Tumour stem cells--a new concept in tumour biology].

There is growing evidence that tumours display a hierarchy similar to normal tissues. Accordingly, a small population of tumour stem cells is supposed to perpetuate tumour growth. These cells renew themselves and are highly tumourigenic upon injection into immunocompromised animals, yielding tumours largely identical to those from which they were derived. Tumour stem cells exhibit a high degree of chemoresistance due to slow cycling and constitutive expression of multiple members of the ATP-BINDING CASSETTE (ABC) family of transporters. An increasing number of tumours with tumour stem cells has been identified by now, including breast, brain, colon and prostate cancers, as well as leukemias. Detailed characterization of tumour stem cells may contribute to a better understanding of the underlying biology of the respective tumours and lead to novel curative therapies.