I am so sorry for your situation.  Medical Malpractice is one of the most complicated causes of action at times and in some states attorneys must do a tremendous amount of work in order to be able to file a case at all (like providing a doctor's affidavit that says that the circumstances warrant malpractice). But you should without a doubt go and see an attorney for a consultation on this matter.  Consultations are generally free of charge.  The attorney will ask your Father to sign authorizations for medical records to have the matter reviewed.  The stage of the cancer in April of 2009 will have an impact on his prognosis or chance for remission and whether that changed because of the failure to inform you.  Good luck.