Idiopathic light chain dyscrasia--a new distinct entity? Report of a case

Clinical course of light-chain smouldering multiple myeloma (idiopathic Bence Jones proteinuria): a retrospective cohort study

BACKGROUND

Bence Jones proteinuria is a disorder that is defined by the excretion of monoclonal light-chain protein. About 15-20% of patients with multiple myeloma secrete monoclonal light chains only, without expression of the normal immunoglobulin heavy chain, which constitutes light-chain multiple myeloma. The definition, prevalence, and progression of these premalignant phases of light-chain multiple myeloma have not been fully characterised. We aimed to identify a subset of patients with idiopathic Bence Jones proteinuria who had a high risk of progression to light-chain multiple myeloma analogous to that seen in patients with smouldering multiple myeloma.

METHODS

In this retrospective cohort study, we studied all patients seen at the Mayo Clinic (Rochester, MN, USA) within 30 days of diagnosis of idiopathic Bence Jones proteinuria between Jan 1, 1960, and June 30, 2004. Inclusion criteria were monoclonal light chain in the urine (≥0·2 g/24 h), absence of intact monoclonal immunoglobulin (M protein) in the serum, and no evidence of multiple myeloma, light-chain amyloidosis, or other related plasma-cell proliferative disorders. The primary endpoint was progression to symptomatic multiple myeloma or light-chain amyloidosis. We examined the cumulative probability of progression and the association of potential risk factors on progression rates to identify patients with a high risk of progression to multiple myeloma or light-chain amyloidosis.

FINDINGS

We identified 101 patients with idiopathic Bence Jones proteinuria. During 901 total person-years of follow-up, 27 (27%) patients developed multiple myeloma and seven (7%) developed light-chain amyloidosis. The major risk factors for progression were amount of urinary excretion of M protein per 24 h, proportion of bone marrow plasma cells, presence of a markedly abnormal free-light-chain ratio (<0·01 or >100), and reduction of all three uninvolved immunoglobulins. Based on the risk of progression, monoclonal light-chain excretion of 0·5 g/24 h or greater or at least 10% bone marrow plasma cells, or both, in the absence of end-organ damage was used to define light-chain smouldering multiple myeloma. The cumulative probability of progression to active multiple myeloma or light-chain amyloidosis in patients with light-chain smouldering multiple myeloma was 27·8% (95% CI 14·2-39·2) at 5 years, 44·6% (27·9-57·4) at 10 years, and 56·5% (36·3-70·2) at 15 years.

INTERPRETATION

Light-chain smouldering multiple myeloma as defined in this study is associated with a high risk of progression to symptomatic light-chain multiple myeloma, and this subset of patients needs careful observation and could benefit from clinical trials of early intervention.

FUNDING

Jabbs Foundation (Birmingham, UK), US National Cancer Institute, and Henry J Predolin Foundation (Madison, WI, USA).

Monoclonal free light chains in urine and their significance in clinical diagnostics: are they really tumor markers?

Bence Jones proteins (monoclonal free light chains of immunoglobulins) are the earliest known biological markers of malignant cell dyscrasia; Bence Jones proteinuria is also present in many types of B cell-related neoplasms. Sometimes, it may also occur in Hodgkin's disease. In some cases, benign monoclonal gammapathy was found to be associated nontumorous diseases as well. The type of monoclonal light chain, the degree of polymerization, and the isoelectric point of the molecule may affect the course of the disease. Urine samples from 637 patients with true or suspected lymphoproliferative diseases were investigated over a 2-yr period by different immunochemical methods. Bence Jones proteinuria was identified in 71 cases by isoelectric focusing combined with immunofixation, while the pathological protein was detected only in 63 cases by conventional methods. Bence Jones proteins can be detected by this new method at a level below the sensitivity of conventional procedures. Bence Jones proteins in the urine may signal a malignant tumor or malignant transformation of an earlier disease. The early detection of monoclonal immunoglobulin light chains in the urine may be important in clinical diagnosis, therapy, and follow-up.

"Idiopathic" Bence Jones proteinuria: long-term follow-up in seven patients

We studied seven patients with idiopathic Bence Jones proteinuria (excretion greater than 1.0 g per 24 hours) who did not have acquired Fanconi's syndrome or an intact monoclonal immunoglobulin in the serum. None had evidence of overt multiple myeloma, of its variants, of systemic amyloidosis, or of malignant lymphoproliferative diseases when the proteinuria was recognized. In three of the seven patients, symptomatic multiple myeloma (associated with systemic amyloidosis in one) developed 8.8 to 21.1 years later. A fourth patient has asymptomatic myeloma and has not been treated. A fifth patient had an evolving myeloma at nine years but died of an unrelated cause. The remaining two patients still have apparently benign Bence Jones proteinuria after 7.7 and 12 years. Plasma-cell labeling indexes were low in all cases tested. This experience shows that although idiopathic Bence Jones proteinuria may remain stable for years, multiple myeloma or amyloidosis often develops, and consequently these patients must be kept under observation indefinitely.