The invention relates to a serotonin receptor (5-HTR) inhibitorselected from the group consisting of a type 1 5-HTR inhibitorand a type 2 5-HTR inhibitorfor use in the prevention and/or treatment of a haematological malignancy. Additionallly the invention relates to in vitromethods for the identificationor isolation of a malignant cell from a haematological malignancy or for diagnosing a haematological malignancy based on detecting the expression of type 1 5-HTR and/or type 2 5-HTR.Furthermore the invention relates to in vitromethods for determining the prognosis for monitoring the effect of a therapy or for designing a customized therapy in a subject suffering from a haematological malignancy based on determining the levels of type 1 5-HTR and/or type 2 5-HTR.
