Monoclonal Gammopathy of Undetermined Significance (MGUS) Does Not Affect Outcomes in Patients Undergoing Solid Transplants.

Monoclonal gammopathy of undetermined significance (MGUS) results arises from a clonal proliferation of differentiated plasma cells and is a necessary precursor to development of multiple myeloma and some other B cell malignancies. Despite a high incidence in the general population (1-2% of adults in the 6^th and 7^th decades) and increased relative risk for later malignancy, there are few reports about the clinical course and prognosis of MGUS in long-term immunosuppressed patients. We aimed to evaluate the significance of MGUS in patients undergoing solid transplants in terms of clinical outcomes and rate of transformation to secondary B cell malignancy.

We reviewed the medical records of 1493 patients on which kidney (living donor related, living donor-unrelated and deceased donor), liver and pancreatic transplants were performed at Mayo Clinic Arizona, between January 1, 1999 and July 31, 2009 to determine the incidence of MGUS and to further evaluate long-term follow up. At MCA patients are routinely screened using SPEP and for those where an M-spike is detected or suspected immunofixation is required for confirmation. MGUS was defined as previously reported. Patients who had anemia unrelated to their PCD were included.

Patients were observed until death or, for those still alive, until July 2009. The major goal of the study was to assess the impact of MGUS on transplant outcomes and progression to active myeloma or related disorders. Patients who did not experience progression were censored at the time of last follow-up. Nominal variables were compared using Fisher's exact test. A two-tailed P value less than .05 was considered significant.

In this series, SPEP was performed in 1199 out of 1593 cases (75%) before transplantation. The most common abnormalities detected by SPEP included a normal pattern (70%), polyclonal pattern (16.8%), hypoalbuminemia (8%), hypogammaglobulinemia (2.4%) and the presence of M spike (2.8%). Immunofixation revealed the presence of a monoclonal immunoglobulin in 34 patients: IgG 30 cases (88%), IgM in 2 (6%) and biclonal disease in 2 (6%). The median age at diagnosis of MGUS was 60 years (range, 46 to 84 years), and included 63.7% of males. Clinical characteristics of the MGUS cases are seen in Table 1. Two MGUS patients were diagnosed only after the transplant was performed (338 and 1082 days respectively). There was no association between post-transplant lymphoproliferative (PTLPD) and MGUS and even when some MGUS patients died (7/34, 20%) death was not associated with progression of the monoclonal clone or development of a PTLPD or other malignancy. MGUS does not impact transplant outcomes. PTLPD disorders developed in 6 cases and none was associated with a MGUS. After a median of 88 months no MGUS patient developed transformation to active myeloma or a related disorder. Overall survival after transplantation was not significantly different among MGUS and Non- MGUS cases (6.48 vs 8.36 years p>0.05).

Despite the frequency of MGUS in the general population there are few studies which have assessed MGUS in solid organ transplant patients. An increased incidence of monoclonal gammopathy in patients with autoimmune disease and in older non-transplant populations suggests that impaired immunity might lead to development of MGUS and later monoclonal B-cell malignancies. Interestingly, we identified two cases where MGUS appeared after transplant. In this series, we report on the incidence and follow/up of MGUS in patients screened before transplantation. The primary outcome for transplant recipients is unaffected by the presence of MGUS and incidence is in accordance with the expected frequency (2.8%). Patients with MGUS do not appear to be at risk for progression due to chronic immunosuppression. Testing for MGUS before transplantation is not cost-efficient and therefore would not be recommended. To our knowledge this is the largest series of MGUS and transplant outcome yet reported.

Stewart:Takeda-Millenium, Celgene, Novartis, Amgen: Consultancy; Takeda, Millenium: Research Funding; Genzyme, Celgene, Millenium, Proteolix: Honoraria.