If more than 2 DLTs occur during the treatment period of the first four treated patients, then the enrolment of additional patients will be stopped. In addition, in case of a life threatening (grade 4) adverse reaction enrolment and treatment of ongoing patients will be immediately discontinued. In both cases, enrolment will only be resumed upon the decision of the sponsor if the Data Safety Monitoring Board can conclude that the causality of the event was unrelated or unlikely related to study treatment.