The present invention relates to pyrrolobenzodiazepines (PBDs), in particular compound B (a PBD dimer) and salts and solvates thereof, as well as conjugates thereof with a cell binding agent. The conjugates of the invention may be used to provide an active PBD compound at a target location. The target location is preferably a proliferative cell population. The antibody is preferably an antibody for an antigen present on a proliferative cell population. The invention also or alternatively provides a pharmaceutical composition comprising the conjugate and/or use of the conjugate in the preparation of a medicament for use in the treatment of a cancer which is chronic myeloid leukaemia or a lymphoma.
