Increase of dFLC from the nadir reached after up-front therapy in 20 patients with cardiac progression. Cardiac progression is defined by an increase in NT-proBNP that is both >30% and >300 ng/L. Red bars: >10% increase in dFLC. Blue bars: “high-risk dFLC progression,” defined as an increase in dFLC that is >20 mg/L, >20% of baseline value observed at diagnosis, and >50% of the value reached at best response.