A method of measuring Gadd45β expression comprising the step of measuring Gadd45β expression levels in a sample of cells, for example CD 138 expressing cells, obtained from a subject known to have or suspected of having a haematological malignancy. Expression levels may be used in diagnosis, for example of multiple myeloma, in providing a prognosis, for example in a patient having multiple myeloma or in guiding selection of an appropriate treatment agent, especially a treatment agent comprising Gadd45β and or MKK7 inhibitors. Also datasets comprising measured expression levels from multiple subjects.