<p>The invention relates to an in-vitro method for predicting the likelihood that a patient suffering from a thoracic tumor will respond to the treatment with an Eg5 inhibitory compound by determining the expression level of the eg5 gene or Eg5 protein as biomarker in a tissue sample from the patient, wherein a higher expression level of the eg5 gene or Eg5 protein indicates that the patient is likely to respond to the treatment compared to a reference value. Another object of the invention concerns a method for monitoring a thoracic tumor, which is associated with Eg5 expression, by administering an effective amount of at least a single Eg5 inhibitor to a mammal in need of such treatment and determining the Eg5 expression in a biological sample withdrawn from the mammal, and wherein a decrease in Eg5 expression indicates an increased likelihood that the mammal responds to the treatment with the inhibitor. The invention also relates to the use of Eg5 as biomarker for rare thoracic tumors.</p>
