MRD Testing: Have We Found the Method We Need?

After more than10 years of progress in myeloma treatment due to the introduction of the novel therapies, researchers now need to know how to eliminate the myeloma cells that remain after current therapies. Today, we are on the brink of having a test that will help us have a clear plan to eradicate residual disease.

The new highly sensitive and extremely accurate flow cytometry test developed with the support of the IMF's Black Swan Research Initiative by Spanish researchers is that test.

It is proving itself to be the most affordable, most sensitive, most easily accessible MRD test yet, and earned near-unanimous acclaim from researchers at a flow workshop co-hosted by the IMF at Memorial Sloan Kettering Cancer Center (MSKCC) in July, as I reported in my blog here.  Asked by an audience member, "Can one of the fluorescent dyes (fluorochromes) used in the FLOW MRD test be changed or improved?" Dr. Alberto Orfao, the FLOW MRD test developer from Salamanca, Spain, said, "Of course - possibly yes!" But these types of tweaks can be never ending, added Dr. Orfao.

 "Do we have a test right now which is working very well? The answer is: YES," said Dr. Orfao. "It is standardized, reliable and sensitive enough at the 10^-5 level. Nothing more is needed. It is time to stop tweaking and move forward with full validation in patient trials!"

As readers of this blog are no doubt aware, some in the myeloma community argue that we need a DNA sequencing [molecular] test for MRD in the bone marrow. The main potential advantage of the molecular test, they contend, is greater sensitivity versus flow. However, the new flow method is now equally sensitive and provides excellent prediction of very good patient outcomes. I would add that a more sensitive test might encourage overly aggressive, unnecessary treatment, causing more harm than good!

To be sure, careful comparisons of molecular and flow testing are essential. But after careful consideration of all the pros and cons of each method, the IMF's Black Swan Research team has chosen Flow MRD as the primary MRD detection method--as the benchmark for comparison with other methods.

On the pro side, an important benefit of the new flow method is that it utilizes a stored computer database of all possible myeloma clones or subclones for instant comparison and classification. All myeloma clones or subclones can be identified by flow methodology at any point during the course of the disease. Conversely, the DNA "dominant clone" approach risks missing minor subclones, which take over later in the disease. If residual subclones are identified, these can be characterized and sorted one by one with the flow method for detailed studies, including full sequencing of the DNA.  Applying DNA technology in this combined flow/ molecular fashion is simple and very informative.

The new flow method allows careful measurement of myeloma at the very low levels of disease needed to predict excellent outcomes and enhance treatment for some patients to achieve an MRD-Negative status.

Since the flow test is standardized, widely available and cheap, there is no longer a need for another method such as the molecular method, which has a number of disadvantages. One limitation of the molecular method is that the bone marrow from the time of diagnosis (or a new relapse) is needed to identify the "dominant or main clone" for future monitoring. In my opinion, the molecular method has other disadvantages. It is more expensive--estimates range between $750 and $1,000 (compared to between $100 and $150 for the new flow test)--and cannot be performed at the local center. To those who would argue for using both the molecular and flow tests, a practical point to keep in mind is that "splitting" bone marrow samples into two parts, one for flow and one for molecular, is not ideal. For the best results, the flow test needs the maximum number of myeloma cells from the "first pull" from the bone marrow aspiration sample to give the most accurate results.

Thus, although it is important to compare the flow and molecular methods in some trials, it seems likely that flow is all that we need! Moving forward, there can be some "fine-tuning," with the addition of the Hevylite ratio test as a quantitative replacement for immunofixation (IFE) and whole body PET/CT to directly evaluate myeloma disease outside the bone marrow.

So stay tuned as the Black Swan Research Initiative moves rapidly forward to achieving chronic disease control and a cure!

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