Table 1 Plasma cell leukemia response criteria by the International Myeloma Working Group.

Response	Serum and urine biomarkers^a	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 immunofixation^b	<5% by morphology	Negative by morphology	Absent
Very good partial response	≥90% reduction of serum M-protein & <100 mg/24 h urinary M-protein^c	<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 h^d	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.

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