In this trial up to 200 patients with either λ light chain (LC) monoclonal gammopathy of undetermined significance (MGUS) or λ LC smoldering multiple myeloma (SMM) with a κ::λ LC ratio < 0.26 and whose λ minus κ LC difference (dFLC) is greater than 23 mg/L will be recruited. Heavy chain type will not affect patient eligibility as long as the involved LC is λ type.