Table 1.

Plasma cell leukemia response criteria by the International Myeloma Working Group.

Response	Serum and urine biomarkersa	BM plasma cells	Peripheral blood plasma cells	Extramedullary disease
Stringent complete response (CR)	Negative serum & urine immunofixation; Normal serum-free light chain ratio	<5% by morphology & no malignant plasma cells by flow cytometry	Negative by morphology & flow cytometry	Absent
Complete response	Negative serum & urine immunofixationb	<5% by morphology	Negative by morphology	Absent
Very good partial response	≥90% reduction of serum M-protein & <100 mg/24 h urinary M-proteinc	<5% by morphology	Negative by morphology	Absent
Partial response	≥50% reduction of serum M-protein & reduction in 24 h urinary M-protein by ≥90% & <200 mg/24 hd	5–25% by morphology	1–5% plasma cells by morphology	≥50% size reduction from baseline
Stable disease	Not meeting the criteria of either partial response or progressive disease
Progressive disease	>25% increase in the level of the serum M-protein with an absolute increase ≥5 g/L;>25% increase in the 24 h urinary light chain excretion with an absolute increase ≥200 mg/24 h	>25% increase or absolute increase ≥10%	>5% absolute increase in plasma cells by morphology	Increase in size or number
Relapse from CR	Reappearance of original M-protein in serum and/or urine immunofixation	>10% increase	Detectable at any level	Any extramedullary disease

^aIt should be maintained for a minimum of 6 weeks. In case of discrepancy or undetectable serological parameter, the patient must be classified according to bone marrow criteria.

^bIf the serum and urine M-protein are unmeasurable, a normal serum kappa/lambda ratio is also required.

^cIf the serum and urine M-protein are unmeasurable, a ≥90% decrease in the difference between involved and uninvolved light chains is required.

^dIf the serum and urine M-protein are unmeasurable, a ≥50% decrease in the difference between involved and uninvolved light chains is required.