A Pre-Existing Plasma Cell Disorder Occurs in Most Patients with Multiple Myeloma.

Background. A pre-existing plasma cell disorder (PPCD), such as monoclonal gammopathy of undetermined significance (MGUS), is thought to be present in at least one-third of patients presenting with symptomatic multiple myeloma (MM). However, no study has comprehensively evaluated the proportion of patients with MM that had a PPCD by laboratory testing on pre-diagnostic sera.

Methods. The Walter Reed Army Medical Center autologous stem cell transplant database was cross-referenced with the Department of Defense Serum Repository (DoDSR) database, which catalogs serum samples collected every 2 years on over 4 million active-duty service members. All samples ³2 years prior to the diagnosis of MM were retrieved. Serum protein electrophoresis (SPEP), immunofixation electrophoresis (IFE) and serum free light chain analysis (sFLC) (The Binding Site, San Diego, CA) were performed on all samples. A PPCD was defined as a positive SPEP, IFE or abnormal sFLC ratio.

Results. Serum samples prior to the diagnosis of MM were available for 30/90 patients, and the median number of samples per patient was 3.5 (range, 1–14). The median age at diagnosis of MM was 48.1 yrs (29–67), with 96% male, 53% Caucasian, and 47% African-American. The Ig isotype of MM was IgG 76%, IgD 10%, light-chain 7%, and non-secretory 7%. A PPCD was detected in 27/30 patients (90%, 95% CI 74–97%). The initial PPCD was detected by sFLC alone in 6/27 (22.2%), IFE alone 2/27 (7.4%), SPEP+IFE 5/27 (18.5%), SPEP+IFE+sFLC 13/27 (48.1%) and IFE+sFLC 1/27 (3.7%). There were 4 patients whose only positive sera was 2.5–3.5 years prior to diagnosis, with all preceding sera negative.

Conclusions. First, a pre-existing plasma cell disorder is present in most MM patients at least 2.5 years prior to diagnosis. Second, consistent with published evidence for a small fraction of patients with high risk MGUS, 4/30 patients were documented to progress rapidly through an MGUS phase to MM. Third, 4/4 patients with light chain only or non-secretory MM had a PPCD that was detected only by sFLC, thereby indicating that all these tumors are preceded by a light chain only or non-secretory PPCD.