Gamma Gap Measurement: Tracking Treatment Response in Multiple Myeloma
Posted: Monday, May 18, 2020
In patients with multiple myeloma, measuring the gamma gap could be a rapid, inexpensive, point-of-care method to assess disease burden and response to treatment, according to results of a retrospective chart review study published in JCO: Oncology Practice. The gamma gap is the calculated difference between a patient’s total serum protein and albumin, which can be determined from a standard comprehensive metabolic profile.
Megan M. Dupuis, MD, PhD, of MD Anderson Cancer Center, Houston, and colleagues correctly “hypothesized that the gamma gap correlates with the level of serum monoclonal immunoglobulins (serum M-spike)…at the time of diagnosis (before treatment), during treatment, and at the end of treatment,” they wrote. They proposed it could be used as a point-of-care test that would complement—although not ultimately substitute for—“the gold standard for measurement of the M-spike, serum protein electrophoresis (SPEP) and immunofixation.” SPEP results take several days to come in, whereas gamma gap results typically may be available in 1 hour. A clinician’s “ability to quickly make informed treatment decisions could ameliorate the anxiety patients currently experience” while waiting for SPEP results, the investigators proposed.
The review included charts of 393 patients. The gamma gap highly correlated with the level of M-spike, “and the change in gamma gap correlated with myeloma treatment response,” noted the authors.
SPEP and immunofixation are usually ordered before initiation of therapy and with each subsequent cycle of therapy, the team continued. These processes “require equipment and experience that may not be available in all laboratories,” so gamma gap measurement could be “of particular importance in resource-poor areas.” However, it is relevant also “to even the most sophisticated laboratories because of [the] more rapid turnaround time…. In primary care settings, using the gamma gap as a screening test may help to increase the pretest probability of a positive SPEP and decrease [its] unnecessary use.”
Disclosure: The study authors’ disclosure information can be found at ascopubs.org.