I think recovery suggests getting better where as a successful treatment suggests that the treatment works as expected. A treatment may make no claims of recovery but just suppress or reduce certain symptoms if this works it can be classed as successful even if it doesn't lead to recovery. I view remission as an admission that the disease mechanism is suppressed but could come back. Oncologists will often talk of remission as they know there is a chance that cancer will reoccur over the next few years for someone who they have treated and who appears clear of the disease. Without a good understanding of disease mechanism or massive long term follow up I would have thought remission is a more honest phrase than recovered.