For a MM patient with a monoclonal intact immunoglobulin at diagnosis, “light chain escape” or “FLC escape” is the term used to describe disease relapse with just monoclonal FLC production. This is examined in more detail in Section 18.2.1 but here, the prognostic implications of FLC escape are considered.
A study of 104 patients who relapsed after bortezomib-based salvage therapy  found that 15 (14%) relapsed with an altered disease phenotype, of whom 9 (9%) had plasmacytoma/plasma cell leukaemia and 6 (6%) showed FLC escape. The transformed group had significantly worse median overall survival (10.7 vs. 32.7 months; p<0.001) (Figure 20.6). A separate investigation of relapse in 232 patients  reported changes of immunoglobulin production in 39 (17%) patients, of whom 15 (6%) had FLC escape and 7 (3%) had monoclonal immunoglobulin escape. Both of these groups had similarly short survival after the change in production (approximately 3 months).
Brioli and colleagues  have published the largest analysis of clonal change at relapse to date, and reported that 10.4% (54/520) IIMM patients relapsed with FLC escape, 35.2% (183/520) relapsed with rising intact immunoglobulin plus FLC, while 49.6% (258/520) relapsed with significant rises in their intact immunoglobulin alone. Interestingly, they found that patients who relapsed with FLC alone or FLC plus immunoglobulin had similarly reduced survival after relapse compared to those without rising FLC (p=0.002; Figure 20.7). Tacchetti et al.  reported FLC escape in a similar proportion of patients (10%). The authors also confirmed the prognostic significance of disease relapse characterised by an increase in sFLCs, with or without an associated increase in serum monoclonal protein. Increasing sFLCs predicted an imminent risk of progression with end organ damage in 70% of cases, and on multivariate analysis, an involved/uninvolved sFLC ratio ≥120 at relapse was an independent variable that predicted a shorter time to second progression (HR: 7.26). The authors conclude that these findings confirm the value of monitoring patients with sFLC measurements after treatment with novel agent-based therapies.