There is no firm guidance on this point: it is up to the discretion of the doctor, as long as he/she is acting in accordance with generally accepted standards of care, in the patient's interests. There is a difference of opinion on this subject: some doctors feel that you have to be open and transparent, so that patients can settle their affairs, have a chance for closure or accomplish their "bucket list," etc. Other doctors feel that by lying or hiding the severity, you keep the patient's morale and spirits up, which can boost the immune system and health and increase the chance of overcoming the disease, or at least living longer. Since there is a legitimate difference of medical opinion about this, it is not likely wrong for your doctor to have done what he/she did.