Myeloma expert Dr. Betsy O’Donnell reviews the terms that define myeloma treatment response, such as complete remission (CR) and partial remission (PR). Dr. O’Donnell goes on to discuss the new tools that are being used to monitor treatment effectiveness, including MRD (minimal residual disease).
Dr. Betsy O’Donnell is Assistant Professor of Medicine at the Dana-Farber Cancer Institute specializing in Plasma Cell Disorders.
Dr. O’Donnell, Alex wrote in with this question. “What is the difference between a complete response, VGPR, and PR as it applies to prognosis and maintenance after an autologous stem cell transplant?” And before you answer the question, would you define VGPR and PR for us?
Dr. Betsy O’Donnell:
Sure. So, we have different criteria that help us understand how well a drug is working, and they’re uniformly used across clinical trials so that we’re all speaking the same language. And so we talk about a PR, a VGPR, and a CR. So, a CR is a complete response, which is 100 percent of that monoclonal protein that we initially detected is gone. We can’t measure it. Or if you have an elevated light chain, which is another piece of the protein, that has gone back down to normal.
Taking that a step further, astringent CR is if we do a bone marrow biopsy and we can’t find any cancer plasma cells in there. A VGPR is where we see a 90 percent reduction in the amount of protein we can measure, and a PR is anything over – a partial response is anything over 50 percent.
So, that’s a language we speak really just so that when we’re interpreting clinical trials, we all are using the same criteria.
And so these are different terms that classify it. If the example that you gave, someone’s had a transplant, what would typically happen 100 days after that transplant is a patient would restart maintenance therapy.
The classic maintenance is just lenalidomide (Revlimid), which is the pill that they were probably taking before that. And there’s a lot of controversy now but no good answers about changing therapy after a transplant, if you haven’t received a deep response.
What we do know is that after a transplant, when someone goes on lenalidomide maintenance, they continue to respond. So, the greatest depth of response is not necessarily achieved in the induction phase or right immediately after transplant, but over time on maintenance.
There’s another tool that we’re now using and incorporating, both in terms of how we assess treatment but also potentially in how we modify treatment, which is something called minimal residual disease, MRD, which goes a step beyond. When people have astringent CR, a CR, looking for really just traces of the disease on a molecular level.
And all of those help us understand how well the patient has responded and how long that remission might last, but they’re not definitive in terms of how we should adjust treatment based on those right now.