plasma cell leukemia ( pcl ) was originally defined by the presence of both > 20% circulating plasma cells ( pcs ) and an absolute count > 2  10/l pcs , although in many studies the presence of only 1 of the above criteria was required . pcl may be classified as primary when it presents de novo in patients without previous evidence of multiple myeloma ( mm ) or secondary when it is presented as a leukemic transformation of a previously recognized mm . primary pcl is a rare entity with an incidence of 2 to 4% of mm and is associated with a worse prognosis than mm . however , with the use of novel drugs upfront , median survival ranging from 18 to 36 months has been reported . the presence of circulating pcs , identified by cytology , multiparameter flow cytometry or slide - based immunofluorescence , is also associated with a worse prognosis in myeloma patients not fulfilling the criteria of pcl . the presence of circulating pcs is also a risk factor of progression to active disease in patients with monoclonal gammopathy of undetermined significance and smoldering mm . it has been suggested that mm patients with circulating pcs , even below 20% , could have the same bad prognosis as patients with pcl . indeed , a lower cutoff of 5% or 0.5 10/l of nucleated peripheral blood cells to redefine pcl has been proposed . in the present study , the impact of the presence of circulating pcs assessed by cytology on the survival of patients with mm was analyzed . requirements to enter the study were a diagnosis of symptomatic mm or primary pcl according to the international myeloma working group ( imwg ) criteria between january 2008 and december 2013 in 5 university hospitals from catalonia , and to have peripheral blood smears at diagnosis available for review . the study was approved by the ethic committee of the hospital de la santa creu i sant pau and was conducted according to the declaration of helsinki . clinical data including age , sex , myeloma isotype , percentage of bone marrow plasma cells , lactate dehydrogenase ( ldh ) , durie - salmon and iss stages , as well as initial treatment and follow up , were collected from medical records . cytogenetic analysis was performed according to local policies and patients were treated according to regional protocols . wright - giemsa stained peripheral blood smears were reviewed by 5 experienced hematologists on peripheral blood cytology . each sample was analyzed by a single morphologist , with each following the same common criteria . the primary endpoint was overall survival ( os ) measured from the date of diagnosis to the date of death or last follow up . differences in demographics and baseline characteristics were compared using the two - sided fisher s exact test for categorical variables and the mann - whitney u test for continuous variables . survival analysis was performed using the kaplan - meier method and differences were tested for statistical significance using the log - rank test . the study cohort included 482 patients diagnosed with mm between january 2008 and december 2013 . the median age at diagnosis was 69 years ( range 28 to 92 years ) . the median follow up was 28 months for the whole cohort and 38 months for the patients alive . first - line therapy was based on bortezomib combinations in 230 ( 47.7% ) patients , alkylating agents with glucocorticoids in 114 ( 23.7% ) patients , vincristine , doxorubicin ( adriamycin ) , and dexamethasone ( vad ) or vad - like chemotherapy in 60 ( 12.4% ) , immunomodulatory - based combinations in 26 ( 5.4% ) , high - dose dexamethasone in 4 ( 0.8% ) , and only palliative care in 48 ( 9.9% ) patients . one hundred and fifty - six ( 32.4% ) patients received autologous stem cell transplantation as part of their first - line treatment . twelve ( 2.5% ) patients received allogeneic stem cell transplantation during the course of the disease . clinical characteristics at diagnosis according to the circulating pcs group are summarized in table 1 . differences in age , sex , myeloma isotope , ldh , durie - salmon and iss stages between the 4 groups were not statistically significant . however , patients within the 5 to 20% circulating pcs group had lower platelet counts ( median 8610/l vs. 21410/l , p<0.0001 ) and a higher proportion of bone marrow pcs ( median 53% vs. 36% , p=0.004 ) . the 5 patients with > 20% circulating pcs were initially treated with bortezomib and dexamethasone ( 2 patients ) ; bortezomib , cyclophosphamide and dexamethasone ( 1 patient ) ; melphalan and prednisone ( 1 patient ) ; and bortezomib , melphalan and prednisone ( 1 patient ) . of the 12 patients with 520% circulating pcs , 1 died the day after diagnosis and only received supportive care , the remaining 11 patients were initially treated as follows : bortezomib and dexamethasone ( 6 patients ) ; bortezomib , thalidomide and dexamethasone ( 2 patients ) ; vad ( 1 patient ) ; bortezomib , melphalan and prednisone ( 1 patient ) ; and cyclophosphamide and steroids ( 1 patient ) . one patient with > 20% circulating pcs and 3 patients with 520% circulating pcs received an autologous stem cell transplantation as consolidation . according to the percentage of circulating pcs , 4 groups were considered for the analysis of survival : no circulating plasma cells , 382 ( 79.2% ) patients ; 1 to 4% circulating plasma cells , 83 ( 17.2% ) patients ; 5 to 20% circulating plasma cells , 12 ( 2.5% ) patients ; and classical pcl group ( > 20% or > 210/l plasma cells ) , 5 ( 1% ) patients . a patient with 15% circulating pcs but an absolute circulating pc count of 2.710/l the median os of patients with no circulating pcs , 1 to 4% , 5 to 20% and > 20% were 47 ( 95%ci 38.655.4 ) months , 50 ( 95%ci 31.068.9 ) months , 6 ( 95%ci 0.911.1 ) months and 14 ( 95%ci 9.718.3 ) months , respectively ( figure 1 ) ( p<0.001 ) . overall survival according to the circulating plasma cells ( pcs ) group in patients with multiple myeloma ( p<0.001 ) . in the univariate analysis , the other factors associated with a worse survival together with circulating pcs were age older than 65 years at diagnosis , creatinine > 2 mg / dl , treatment with new drugs upfront ( proteasome inhibitors or immunodulatory drugs ) , and durie - salmon and iss advanced stages . cytogenetic data was not included in the survival analysis due to the lack of such data in most patients . the finding of 5 to 20% circulating plasma cells , age older than 65 years , durie - salmon iii , creatinine > 2 mg / dl , and iss 3 retained their significance in the multivariate analysis ( table 2 ) . two hundred and sixty five of the 482 ( 54.9% ) patients were treated upfront with proteasome inhibitors and/or inmunomodulatory drugs . of these , 192 ( 72.5% ) patients had 0% circulating pcs , 61 ( 23.0% ) patients had 1 to 4% circulating pcs , 9 ( 3.4% ) patients had 5 to 20% circulating pcs and 3 ( 1.1% ) patients had a diagnosis of classical pcl . one hundred and ten ( 41.5% ) patients treated with novel agents upfront died during follow up and their median os was 50 ( 95% ci 3861 ) months . in patients treated with novel agents upfront , the median os in cases with 0% , 1 to 4% , 5 to 20% and pcl were 58 ( 95% ci nr ) months , 60 ( 95% ci 3386 ) months , 22 ( 95% ci 065 ) months and 14 ( 95% ci 126 ) months , respectively . when only 2 groups were considered , < 5% and 5% circulating pcs , median os were 58 ( 95% ci 46  69 ) months and 14 ( 95% ci 0.4  27 ) months ( figure 2 ) . overall survival according to the circulating plasma cells ( pcs ) in patients with multiple myeloma and plasma cell leukemia ( pcl ) treated with novel drugs upfront ( p<0.001 ) . together with the percentage of circulating pcs , the other factors associated with a worse os in univariate analysis were creatinine > 2mg / dl and iss stage ii or iii . a trend was observed in patients > 65 years old and durie - salmon stage iii . taking into account the aforementioned variables , having 5% circulating pcs alone was the only fact which maintained statistical significance in the multivariate analysis ( table 3 ) . ldh was not included in the multivariate analysis due to the lack of statistical significance or even a trend in univariate analysis ( rr 1.1 , 95% ci 0.71.9 , p=0.467 ) . the study cohort included 482 patients diagnosed with mm between january 2008 and december 2013 . the median age at diagnosis was 69 years ( range 28 to 92 years ) . the median follow up was 28 months for the whole cohort and 38 months for the patients alive . first - line therapy was based on bortezomib combinations in 230 ( 47.7% ) patients , alkylating agents with glucocorticoids in 114 ( 23.7% ) patients , vincristine , doxorubicin ( adriamycin ) , and dexamethasone ( vad ) or vad - like chemotherapy in 60 ( 12.4% ) , immunomodulatory - based combinations in 26 ( 5.4% ) , high - dose dexamethasone in 4 ( 0.8% ) , and only palliative care in 48 ( 9.9% ) patients . one hundred and fifty - six ( 32.4% ) patients received autologous stem cell transplantation as part of their first - line treatment . twelve ( 2.5% ) patients received allogeneic stem cell transplantation during the course of the disease . clinical characteristics at diagnosis according to the circulating pcs group are summarized in table 1 . differences in age , sex , myeloma isotope , ldh , durie - salmon and iss stages between the 4 groups were not statistically significant . however , patients within the 5 to 20% circulating pcs group had lower platelet counts ( median 8610/l vs. 21410/l , p<0.0001 ) and a higher proportion of bone marrow pcs ( median 53% vs. 36% , p=0.004 ) . the 5 patients with > 20% circulating pcs were initially treated with bortezomib and dexamethasone ( 2 patients ) ; bortezomib , cyclophosphamide and dexamethasone ( 1 patient ) ; melphalan and prednisone ( 1 patient ) ; and bortezomib , melphalan and prednisone ( 1 patient ) . of the 12 patients with 520% circulating pcs , 1 died the day after diagnosis and only received supportive care , the remaining 11 patients were initially treated as follows : bortezomib and dexamethasone ( 6 patients ) ; bortezomib , thalidomide and dexamethasone ( 2 patients ) ; vad ( 1 patient ) ; bortezomib , melphalan and prednisone ( 1 patient ) ; and cyclophosphamide and steroids ( 1 patient ) . one patient with > 20% circulating pcs and 3 patients with 520% circulating pcs received an autologous stem cell transplantation as consolidation . according to the percentage of circulating pcs , 4 groups were considered for the analysis of survival : no circulating plasma cells , 382 ( 79.2% ) patients ; 1 to 4% circulating plasma cells , 83 ( 17.2% ) patients ; 5 to 20% circulating plasma cells , 12 ( 2.5% ) patients ; and classical pcl group ( > 20% or > 210/l plasma cells ) , 5 ( 1% ) patients . a patient with 15% circulating pcs but the median os of patients with no circulating pcs , 1 to 4% , 5 to 20% and > 20% were 47 ( 95%ci 38.655.4 ) months , 50 ( 95%ci 31.068.9 ) months , 6 ( 95%ci 0.911.1 ) months and 14 ( 95%ci 9.718.3 ) months , respectively ( figure 1 ) ( p<0.001 ) . overall survival according to the circulating plasma cells ( pcs ) group in patients with multiple myeloma ( p<0.001 ) . in the univariate analysis , the other factors associated with a worse survival together with circulating pcs were age older than 65 years at diagnosis , creatinine > 2 mg / dl , treatment with new drugs upfront ( proteasome inhibitors or immunodulatory drugs ) , and durie - salmon and iss advanced stages . cytogenetic data was not included in the survival analysis due to the lack of such data in most patients . the finding of 5 to 20% circulating plasma cells , age older than 65 years , durie - salmon iii , creatinine > 2 mg / dl , and iss 3 retained their significance in the multivariate analysis ( table 2 ) . two hundred and sixty five of the 482 ( 54.9% ) patients were treated upfront with proteasome inhibitors and/or inmunomodulatory drugs . of these , 192 ( 72.5% ) patients had 0% circulating pcs , 61 ( 23.0% ) patients had 1 to 4% circulating pcs , 9 ( 3.4% ) patients had 5 to 20% circulating pcs and 3 ( 1.1% ) patients had a diagnosis of classical pcl . one hundred and ten ( 41.5% ) patients treated with novel agents upfront died during follow up and their median os was 50 ( 95% ci 3861 ) months . in patients treated with novel agents upfront , the median os in cases with 0% , 1 to 4% , 5 to 20% and pcl were 58 ( 95% ci nr ) months , 60 ( 95% ci 3386 ) months , 22 ( 95% ci 065 ) months and 14 ( 95% ci 126 ) months , respectively . when only 2 groups were considered , < 5% and 5% circulating pcs , median os were 58 ( 95% ci 46  69 ) months and 14 ( 95% ci 0.4  27 ) months ( figure 2 ) . overall survival according to the circulating plasma cells ( pcs ) in patients with multiple myeloma and plasma cell leukemia ( pcl ) treated with novel drugs upfront ( p<0.001 ) . together with the percentage of circulating pcs , the other factors associated with a worse os in univariate analysis were creatinine > 2mg / dl and iss stage ii or iii . a trend was observed in patients > 65 years old and durie - salmon stage iii . taking into account the aforementioned variables , having 5% circulating pcs alone was the only fact which maintained statistical significance in the multivariate analysis ( table 3 ) . ldh was not included in the multivariate analysis due to the lack of statistical significance or even a trend in univariate analysis ( rr 1.1 , 95% ci 0.71.9 , p=0.467 ) . this study aimed to address the impact of circulating pcs on the survival of patients with mm . seventeen per cent of patients had between 1 and 4% circulating plasma cells . that finding was not associated with other clinical characteristics and had no impact on survival . there was a completely different picture for the 2.5% of patients with 5 to 20% circulating pcs . such patients had lower platelet counts , higher bone marrow infiltration and , importantly , a shorter survival independent of other known clinical prognostic factors . in fact , the median os of 6 months observed in these patients is closer to that of patients with the  classical  definition of pcl . when the analysis was restricted to patients treated with novel agents upfront , the impact of circulating pcs was consistent with the whole cohort . the differences in os observed between patients with 520% circulating pcs and > 20% circulating pcs ( 6 vs. 14 months ) may be explained by the low number of cases in both groups . although the presence of circulating pcs has been previously associated with survival , conventional cytology has been used for their assessment in only one study . in that case , patients with circulating plasma cells constituted 14.1% of the overall series and had a median survival of 25 months . the results of the present study are consistent with the ominous prognostic impact of peripheral blood plasmacytosis ; however , the definition of a high - risk group found was different ; 2% circulating pcs in the study by an et al . and 5% circulating pcs in the study herein . using multiparameter flow cytometry , the presence of circulating pcs has also been associated with survival . in the study from the mayo clinic , such patients had a median os of 32 months versus not reached in patients with 400 or less circulating pcs . in another study from the same institution , which in this case used slide - based immunofluorescence microscopy for plasma cell quantification , 54% of patients with > 4% pcs were identified . these patients had a median survival of 2.4 years compared to 4.4 years in patients with fewer circulating pcs . the aforementioned studies used much more sensitive techniques than those used in the present ; this may explain the different percentages of patients with circulating pcs identified in those studies in comparison with the present one . despite these findings , the definition of pcl has been based on standard morphological examination of peripheral blood . in comparison with flow cytometry and immunofluorescence additionally , conventional cytology has the advantage of being a simple and inexpensive technique that can be applied in any clinical laboratory worldwide . however , it has a limitation ; conventional cytology is not able to identify the clonality of pcs , as can be achieved by flow cytometry and immunofluorescence . this may hamper the specificity of conventional cytology since polyclonal reactive pcs may be rarely detected in some patients with mm . the presence of t(4;14 ) , del(17p ) , amp(1q21 ) and del(1p21 ) in malignant pcs are adverse prognostic factors in mm . indeed , adverse cytogenetics together with iss 3 and/or high ldh identifies a group of patients with an ultra - high risk of mm . several of these genetic abnormalities , particularly del(17p)9 and chromosome 1 alterations are more frequent in pcl than in mm . in the series presented herein , del(17p ) by fluorescence in situ hybridization ( fish ) was observed in 1 of 7 patients with 5 to 20% circulating pcs and 1 of 2 patients with > 20% circulating pcs . a limitation of the present study is that , due to the lack of cytogenetic data in most patients , the prognostic impact of unfavorable cytogenetic abnormalities and the revised iss could not be analyzed . as highlighted in the last consensus by imwg , the diagnosis of pcl has been classically done on the basis of the presence of > 20% circulating pcs and/or an absolute count > 2  10/l pcs . however , lower peripheral blood pc counts , as showed in our study ( that is , 5% peripheral blood plasma cells ) , should be considered as a diagnostic criteria of pcl (  pcl - like  myeloma or early pcl ) , due to the independent and strong prognostic impact . prospective multicenter analysis with translational and correlative studies into the biology of these patients is encouraged as well as risk - oriented therapeutic strategies . careful examination of peripheral blood by conventional microscopy should be done for all patients with mm in daily clinical practice . in conclusion , the presence of 5% circulating pcs by conventional cytology easily identifies a group of patients with myeloma with a prognosis as poor as that of pcl , suggesting that the diagnosis of pcl should be revisited . if confirmed in other series , especially in prospective studies of uniformly treated patients , such patients may benefit from a distinct and more intensified therapeutic approach .
the presence of circulating plasma cells in patients with multiple myeloma is considered a marker for highly proliferative disease . in the study herein , the impact of circulating plasma cells assessed by cytology on survival of patients with multiple myeloma was analyzed . 
 wright - giemsa stained peripheral blood smears of 482 patients with newly diagnosed myeloma or plasma cell leukemia were reviewed and patients were classified into 4 categories according to the percentage of circulating plasma cells : 0% , 14% , 520% , and plasma cell leukemia with the following frequencies : 382 ( 79.2% ) , 83 ( 17.2% ) , 12 ( 2.5% ) and 5 ( 1.0% ) , respectively . 
 median overall survival according to the circulating plasma cells group was 47 , 50 , 6 and 14 months , respectively . at multivariate analysis , 
 the presence of 5 to 20% circulating plasma cells was associated with a worse overall survival ( relative risk 4.9 , 95% ci 2.69.3 ) independently of age , creatinine , the durie - salmon system stage and the international staging system ( iss ) stage . 
 patients with 5% circulating plasma cells had lower platelet counts ( median 86109/l vs. 214109/l , p<0.0001 ) and higher bone marrow plasma cells ( median 53% vs. 36% , p=0.004 ) . 
 the presence of 5% circulating plasma cells in patients with multiple myeloma has a similar adverse prognostic impact as plasma cell leukemia .