Morphologic, immunologic, and cytogenetic (MIC) working classification of the acute myeloid leukemias

Morphologic, Immunologic, and Cytogenetic (MIC) Working Classification of the Acute Myeloid Leukemias Report of the Workshop Held in Leuven, Belgium, September 15-17, 1986 Second MIC Cooperative Study Group* INTRODUCTION

The MIC Workshops grew out of tile realization that a large body of information oil the morphology, immunology, and cytogenetics of the acute leukemias and related disorders had accumulated during the last decade and that such information was of definite diagnostic and prognostic value. Furthermore, the cytogenetic data indicated the existence within hitherto defined morphologic subtypes of leukemias of specific karyotypic anomalies. Concurrent developments in a) immunocytochemical characterization of the leukemias, b) new cytogenetic information in these diseases, and c) the recognition that the FAB classification of the acute leukemiag had critically defined subtypes of acute leukemia led to an almost simultaneous decision on the part of members of the various disciplines to join and coordinate the information, which led to the MIC Workshops and suggested working classifications of these diseases. In the First MIC Cooperative Study Group publication [1] criteria were presented for classification of the acute lymphoblastic leukemias (ALL} utilizing morphologic, immunologic and cytogenetic findings. In this, the second Workshop held in Leuyen (Belgium) in September 1986, all available observations in the acute myeloid leukemias [AML; AML as used here is equivalent to the term ANLL (acute nonlymphocytic leukemia)] were reviewed more specifically. The techniques utilized for morphology, cytochemistry, immunologic identification, and cytogenetics have been recorded in our previous publication, including specific references [1 ].

*This Workshop was organized by Herman Van Den Berghe. Participants in the Second MIC Cooperative Study Group: John M. Bennett (USA), Roland Berger (France), Daniel Catovsky (Great Britain), Georges Flandrin (France), Kenneth A. Foon (USA), Harvey R. Gralnick /USA}, James D. Griffin (USA), Ann Hagemeijer (The Netherlands), Cristina Mecucci (Belgium), Jun Minowada (Japan), Felix Mitelman (Sweden), Jean-Louis Preud'homme (France), Avery A. Sandherg (USA), Herman Van Den Berghe (Belgium).

The following format should be used in referring to this report: Second MIC Cooperative Study Group (1988): Morphologic, Immunologic, and Cytogenetic (MIC) Working Classification of Acute Myeloid Leukemias. Cancer Genet Cytogenet 30:1-15(1988).

1 ¢) 1988 Elsevier Science Publishing Co., Inc. 52 Vanderbilt Ave., New York, NY 10017

Cancer Genet Cytogenet 30:1 15(1988/ 0165-4608/88/$03.50

2

Second MIC Cooperative Study Group Table 1

FAB criteria for AML" Nonerythroid cell component

Cell type in bone marrow

Granulo(:ytes (%)

Monocytes (%)t)

M1 M 2 , M 2 Baso': M3, M3v

< 10 >10 --

<20 --

>.20 <2(1 Variable Variable

>20 >80 Variable Variable

M4, M4Eo '~ M5a, b M6" M71

"More t h a n 30(% of all nucleated bone m a r r o w cells are blasts and less than 50% are erythroid precursors, except fur M6+ J'Promonocytes a n d m o n o c y t e s in M5b; monoblasts in M5a. 'In this form of M2 there is evidence of basophilic granules in the blast (:ells a n d in some of Ihc" m a t u r i n g granulocytic cells in the bone m a r r o w and peripheral blood. 'lln this form of M4 abnormal eosinophilic precursors are presenl. 'More tban 50% erythroid (:ells, often with a b n o r m a l morphology; more than 30% of n o n e r y l h r o i d (;ells are [)lasts. IOften bone m a r r o w is nonaspirable, requiring trephine biopsy. Evidence for megakaryocytic markers is required by monoclona[ antibodies and/or platelet p e m x i d a s e activity (EM).

MORPHOLOGIC SUBTYPES OF AML

The definition of AML by the FAB cooperative group includes the myeloblastic leukemias (M1-M2), p r o m y e l o c y t i c leukemia (M3), m y e l o m o n o c y t i c p r e d o m i n a n t AML (M4), monoblastic p r e d o m i n a n t AML [M5], erythroleukemia (M6), and megakaryoblastic leukemia (M7) (Table 1). In FAB types M 1 - M 6 [2], the use of two or more monoclonal myeloid antibodies will identify over 95% of these cases. This is true, as well, for M7 when reagents against platelet glycoproteins are utilized [3]. Revised criteria for the morphologic classification of AML have been p u b l i s h e d [4], as well as for acute megakaryoblastic leukemia [5]. In these articles a careful and precise distinction was made between M1 and M2; M2 and M4; M5a and M5b; and the modification in the diagnosis of M6 and its separation from m y e l o d y s p l a s i a (MDS). The e m p l o y m e n t of certain cytochemical stains (peroxidase and nonspecific esterase) is a necessary c o m p o n e n t of these classifications [6]. Careful examination and recording of the number and m o r p h o l o g y of basophils and eosinophils should be performed. In addition, we r e c o m m e n d that a careful search be carried out for evidence of myelodysplasia. These findings may be important in the evaluation of some of the specific chromosome abnormalities discussed below. The features of m y e l o d y s p l a s i a have been well described [7]. CYTOGENETICS

For cytogenetic studies it is r e c o m m e n d e d that bone marrow cells be e x a m i n e d directly, as well as following culture for 1-2 days, preferably using a high resolution banding technique. A sufficient n u m b e r of ceils (20-30) has to be karyotyped, in order to detect the presence or absence of cell s u b p o p u l a t i o n s with a normal or abnormal karyotype next to the p r e d o m i n a n t abnormal clones. The glossary and definition of the cytogenetic terms used here is as follows: del

12.0 10.0 6.0 5.0 3.0 1.0 1.0 <0.1 <0.1 <0.1

t(8;21)(q22;q22) t(15;17)(q22;q12) t/del(ll)(q23) inv/del(16)(q22) t(9;22)(q34;q11) t(6;9)(p21-22;q34) inv(3)(q21q26)

t(8;16)(p11;p13) t/del(12)(pl 1-13) +4

M2 M3, M3v M5a (M5b, M4) ~' M4Eo M1 (M2) ~' M2 or M4 with basophilia M1 (M2, M4, M7) b with thrombocytosis M5b with phagocytosis M2 with basophilia M4 (M2) ~

Morphology (FAB)

t'Less frequent associations

"Percentage incidence among AML patients with abnormal karyotypes calculated (m the basis of the information in Mitelman 1985 (16)

Frequency (%)"

T h e MIC c l a s s i f i c a t i o n of AML: K a r y o t y p i c - m o r p h o l o g i c a s s o c i a t i o n s

Karyotypic change

Table 2

M5b/t(8;16) M2 Baso/t(12p) M4/+4

M2/t(8;21) M3/t(15;17) M5a/t(1 lq) M4Eo/inv(16) M1/t(9;22) M2/t(6;9) M1/inv(3)

Suggested MIC nomenclature

¢,O

4

Second MIC Cooperative Study Group

Table 3

The M1C classification of AML: Characteristic c h r o m o s o m e changes without specific morphologic associations

Karyotypic change

Frequency (%)"

Suggested MIC immenclattm?'

+8 - 7 7q 5q Y +21 9q i('l 7q) 20q 22

8.0 4.o 3.0 3.0 1.0 1.0 <0.1 <0.1 <0.1 <0.1

M?/+ 8 M?," 7 M?/7q M?/5q M?/ Y M?/+21 M?/9q M?/i(17(t) M?/20q M ? / + 22

"Sole abnormality among AML cases with chromosome changes. Based on refs. ['16, 171. ~'FAB type to be included, as necessary.

= deletion; t = translocation; inv = inversion; ins = insertion; clone = two cells with the same structural change or additional chromosomes, or three cells with the same missing c h r o m o s o m e In the MIC n o m e n c l a t u r e the FAB classification of the leukemia is placed before the slash mark and the c h r m n o s o m e change characterizing the leukemia after the mark. For example: M2/t(8;21): M3/t(15;17), etc. The number of AML patients in w h o m no c h r o m o s o m e changes are detected varies considerably among laboratories, and the exact incidence will not be established until advanced cytogenetic techniques are utilized uniformly. At present, a realistic estimate would be about one-third of the cases. A m o n g cases with cytogenetic aberrations, about 60% can be accounted for by fhe specific aberrations rev i e w e d at the Workshop (Tables 2 and 3). The frequencies given for the aberrations are only approximations, because they are based on the number of cases reported in the literature and not on systematic prospective studies. A total of 20 characteristic c h r o m o s o m e aberrations were evaluated and established. These are presented in Tables 2 and 3 and their main features are described separately in this report.

B A S I S F O R THE MIC C L A S S I F I C A T I O N

Cytogenetics and Distinctive Morphological

OF A M L

(FAB) S u b t y p e s o f A M L

Specific chromosomal anomalies: t{8,21)(q22;q22). This translocation occurs predominantly in young AML patients and is rare after the age of 50. The bone marrow cells always reveal some degree of granulocytic maturation. Thus, the bone marrow contains large blast cells with abnormally large granules, and a high frequency of thin Auer rods in both the blast cells and maturing granulocytes. These features may be sufficient to predict the specific c h r o m o s o m e change in the majority of cases. Variant translocations occur in 4% of the cases. The t(8;21) (Fig. 1), with or without additional changes, occurs almost exclusively in M2 and makes up 40% of the c h r o m o s o m e abnormalities seen in M2. Additional c h r o m o s o m e changes are

MIC Classification of AML

5

P q q22

nl. ~

~q-

n[ 21

21q,

M2/t(8;21) Figure 1 Schematic presentation of the t(8;21)(q22;q22) associated with an M2 type of AML characterized by the presence of Aner rods in the leukemic cells and favorable response to therapy.

present in about 80% of cases with t(8;21), the great majority being a loss of a sex c h r o m o s o m e (the inactive X in females, Y in males). A n o t h er frequent additional change is 9 q - with an interstitial deletion in w h i c h bands 9q21-q31 are always involved (Table 2). Proposed MIC nomenclature--M2/t(8;21).

t(15;17)(q22;q12). The t(15;17) is confined to M3 and its variant form, and is seen in at least 90% of these cases. The exact breakpoint on c h r o m o s o m e #17 is still an open question. Rare variants occur. About one-third of the patients have + 8 as an additional c h r o m o s o m e change. The promyelocytic form of AML was initially described as hypergranular. A variant form that is hypogranular has been recognized (M3v). Both forms are characterized by the cytogenetic abnormality t(15;17) (Fig. 2). Proposed MIC nomenclature--M3 or M3v/t(15;17).

Figure 2 Schematic presentation of the t(15;17)(q22;q12) in M3 type of AML. This karyotypic anomaly is seen in more than 90% of the cases of APL

q12

q q 22

nt 15

15q,

M3 / f ( 1 5 ; 1 7 )

ni. 17

17q-

6

Second MIC Cooperative Study Group

p22

P

q q23

nt9

der(9)

nil1

der(11)

IVl5a / f ( 9 ; 1 1 ) Figure 3 Schematic presentation of the t(9;11)(p13;q23) seen in cases of M5a acute monoblastic leukemia. The breakpoint on chromosome #11 (q23) is often involved in translocations with chromosomes other than chromosome #9 or is associated with a deletion in M5 types of AML.

t/del(11)(q23). Cytogenetically, this is a heterogeneous group comprising a variety of translocations and deletions, interpreted as terminal as well as interstitial, all with i n v o l v e m e n t of 11q23 (Fig. 3). Among the translocations, the most c o m m o n is t(9;11) with the breakpoint in chromosome # 9 usually at p21-22, followed by t(11;19)(q23;p13), t(10;11)(p11-p15;q23), and t(11;17)(q23;q21-25). These translocations all characterize a group of AML cases with a p r e d o m i n a n t monocytic component; about 50% have M5a morphology. This is also true for cases with deletions at band 11q23, as well as for deletions and translocations involving a more proximal breakpoint (q14). Note that some of these translocations can also be found in disorders presenting as ALL, mostly of the T-cell type. Whether or not these disorders represent different disease entities (different breakpoints?) or bilinear or biphenotypic disorders is still u n k n o w n . The t(4;11)(qll;q23) associated with early pre-B-ALL also involves 11q23 and has been discussed in the MIC 1 report [1]. Acute leukemias with 11q23 rearrangements show an u n u s u a l age distribution: They are most frequently observed in congenital and infant leukemias. Proposed MIC nomenclature--M5a/ t(llq). inv/dell16)lq22 ). This group comprises structural changes of chromosome #16, such as inversions (Fig. 4), deletions and rarely translocations, all with an involvement of band q22. Trisomy 8 is the most frequently occurring additional change. The morphology of M4Eo has been described by several investigators [8, 9]. Emphasis on identifying in the bone marrow the abnormal appearing eosinophils and their granules (e.g., whether they are numerous, large, or magenta in color) is stressed in addition to the M4 criteria. These eosinophilic precursors have aberrant positivity for chloroacetate esterase and often contain PAS-positive granules. Patients with M4Eo/inv(16) (Fig. 4) have a high complete remission rate with standard AML chemotherapy, which may be followed by subsequent central nervous system involvement, often with intracranial (tumor) masses. Proposed MIC nonmnclature-M4EO/inv(16). t(9;22)(q34;q11). The Philadelphia (Ph) chromosome (Fig. 5) is a relatively rare event in AML a n d appears p r e d o m i n a n t l y in M1. In contrast to chronic myeloid

7

MIC Classification of AML

nt 16

inv(16)

M4EO / inv(16) Figure 4 Inversion (breaks at p13 and q22) of a segment of chromosome #16 seen characteristically in an M4 type of AML associated with bone marrow eosinophilia and other unique cellular and clinical features. In some cases a deletion of the long arm of chromosome #16 at band q22 is observed instead of the inversion.

leukemia (CML) where the bone marrow is usually 100% Ph-positive and remains so following therapy, AML cases with the Ph c h r o m o s o m e have a significant population of normal diploid cells at diagnosis with the Ph-positive cells disappearing during remission. Variant Ph translocations also occur in AML. Proposed MIC no-

menclature--M1/t(9;22 ). t(6;9)(p21-22;q34). The exact breakpoint in the short arm of c h r o m o s o m e # 6 has not been established with certainty (Fig. 6). Most patients have an M2 or M4 morphology. There is a strong, but far from absolute, association with bone marrow basophilia. About 20% of patients have a myelodysplastic background. Proposed MIC nomenclature--M2/t(6;9 ]. M1 or M2 or M4/inv(3). Inversion (3)(q21q26) (Fig. 7) has been associated with a variety of de novo AML subtypes (M1, M2, M4, and M7), as well as with AML

Figure 5 Schematic presentation of the genesis of the Philadelphia (Ph) chromosome, most commonly associated with the M1 type of AML. The breakpoints are 9q34 and 22q11.

P qll

n[9

9q+

M1 / t ( 9 ; 22)

n[22

22q-

8

Second MIC Cooperative Study Group

P

p21-22

q q3Z,.

nt6

nt9

6p-

9q+

16'12 / f ( 6 ; 9 ) Figure 6 Schematic presentation of the t(6;9)(p21-22;q34) seen in cases with either M2 or M4 type of AML and often associated with bone marrow basophilia.

seen in the evolution of MDS. Patients whose leukemic cells contain this chromosome abnormality have a relative or absolute thrombocytosis (e.g., a platelet count that is higher than usually seen in the disease or a platelet count >400 x 109/L). In addition to the inversion, other anomalies in this group include insertions and translocations having in c o m m o n the i n v o l v e m e n t of band 3q26. These anomalies, most c o m m o n l y seen in M1, are frequently associated with a relative or absolute thrombocytosis. Proposed MIC nomenclature--M1/inv(3).

Figure 7 Schematic presentation of an inversion of chromosome #3 with breaks at q21 and q26. This anomaly is associated often with the M1 type of AML and thrombocytosis.

P

q

r"

nt 3 M 1 / inv( 3 )

"';

.,2,

inv( 3 )

9

MIC Classification of AML

p 13

P

p11

nt8

8p-

n[16

16p+

MSb/ I-(8;16) Figure 8 Schematic presentation of a newly described t(8;16)(p11;p13,) seen in cases with the M5b wpe of acute monocytic leukemia.

The above m e n t i o n e d three rare subtypes are relatively newly described and await full definition of all their aspects on the basis of more cases.

M5b/t(8;16). A form of M5b has been recognized with the leukemic cells demonstrating significant erythrophagocytosis [10, 11]. This form of M5b is associated with the cytogenetic abnormality t(8;16)(p11;p13) (Fig. 8). Proposed MIC nomenclature--M5b/t(8;16). M2 Baso/12p-. Abnormalities of the short arm of the chromosome #12 ( 1 2 p - ) (Fig. 9) have been found in some patients with untreated AML, MDS or secondary AML. W i t h i n the "de novo" AML category some cases were classifiable as FAB-M4 and others with special features within FAB-M2. These latter cases (M2) have a majority of agranular blasts with other cells showing some evidence of maturation Figure 9

Deletion of the short arm of chromosome #12 (12p-) with a break at band p11.

p11-13

q

nt 12 de[(12 ) M2Baso / f ( 1 2 p )

10

Second MIC Cooperative Study Group

q

nt4

nt4

nt4

M4 /+4. Figure 10 of AML.

Trisomy of chromosome #4 {+4) associated with M4 (and less often M2) type

toward basophils [12]. At least a few of the blast cells have some basophilic granules that are indistinct by light microscopy but more readily identified by electron microscopy (EM). Only a small percentage of the blasts contain peroxidase reactivity. If EM is not available, the myeloid nature of the blast cells should be confirmed by the use of monoclonal antibodies. Proposed MIC n o m e n c l a t u r e - - M 2 Baso/t(12p).

M4 or M2/+4. Trisomy 4 (Fig. 10) is p r e d o m i n a n t l y associated with either M2 or M4 [13, 14]. Proposed MIC Nomenclature--M4~+ 4.

Cytogenetic Anomalies Not Presently Associated with FAB Subtypes Trisomy 8 (+ 8). This is the most c o m m o n cytogenetic anomaly in AML. In addition to being the sole karyotypic change in 8% of AML patients with aberrations, another 11% of the cases have trisomy 8 associated with other chromosome changes. Whereas, + 8 as the sole a n o m a l y is most c o m m o n in M1, M4, and M5 (in that order of frequency), as an additional karyotypic change it is relatively frequent in M3. Monosomy 7 ( - 7) and deletion of 7q (7q - ). Monosomy 7 is the second most common anomaly in AML. However, as the sole anomaly it is seen only in 4% of the cases, p r e d o m i n a n t l y in M2 and M4. Monosomy 7 may be preceded by partial loss of the long arm. In about one-third of cases with del(7q) the breakpoint has been identified at band q22. Both 7 and 7 q - occur with sufficient incidence in patients who received cytotoxic treatment or with k n o w n exposure to toxic agents to warrant a careful and detailed exposure history, in all cases with these chromosomal anomalies.

Deletion of 5q ( 5 q - ) . This anomaly may have variable breakpoints in the long arm of chromosome #5. The total incidence is about 8% of the AML cases; as a sole

MIC Classification of AML

] 1

anomaly it is seen in 3%. In about 25% of the cases in which it is the sole anomaly, the aberration is secondary to cytoxic exposure. - Y . Loss of the Y chromosome in bone marrow cells usually occurs as a normal p h e n o m e n o n of aging in males, particularly in those older than 65 years of age [5]. Its significance as an anomaly in AML remains obscure.

+21,9q-,i(17q),+22. All of these are well documented but rare cytogenetic subtypes of AML, and await further definition on the basis of nlore cases. Immunology The techniques indicated for i m m u n o a n a l y s i s of cell suspensions in the First MIC [1] report are recommended. However, because of the higher expression of Fclg receptors by AML cells, an i n c u b a t i o n step with h u m a n AB serum or immunologlobulin and the use of isotype-identical control antibodies is important. The use of monoclonal antibodies is a necessary c o m p o n e n t for the identification ot each case of acute leukemia, particularly w h e n the appearance of the blast cells is indicative of an undifferentiated cell population in which less than 3% of the blasts show positive peroxidase activity.

Utility of Surface Antigen Analysis in AML A large series of m o n o c l o n a l antibodies has been generated, which identify antigens expressed on the surface of normal and leukemic myeloid cells. The First, Second, and Third Workshops on Leukocyte Differentiation Antigens [18] identified clusters of these antibodies by their reactivity with early and late states of normal hematopoietic differentiation (Table 4). The major value of antimyeloid m o n o c l o n a l antibodies is in establishing or confirming the diagnosis of AML. This analysis should be performed in conjunction with anti-B cell and anti-T cell antibodies, and is particularly useful in situations

Table 4

Cluster designation of m o n o c l o a a l antibodies useful in establishing the diagnosis of AML

Cluster designation

Antibodies~'

B-lineage CD19 CD20

Anti-B4 Anti-B1

T-lineage CD2 CD3 CD5 CD7

Anti-T11, -Leu 5, OKTll Anti-T3, -Leu 4, OKT3, UCHT-1 Anti-T1, -Leu 1, OKT1, T101, 10.2 3A1, WT-1, Anti-Leu 9

Myeloid-Lineage CD11b CD13 CD14 CD15 CD33 "See refs. [18, 19].

Anti-Mol, OKM1 Anti-MCS-2, -MY7 Anti-MY4, -Mo2, -FMC17 FMC10, VIM-D5, DUHL60.1 Anti-MY9, -L4F3

12

S e c o n d MIC C o o p e r a t i v e S t u d y G r o u p

Table 5

D i s t i n g u i s h i n g f e a t u r e s of ALL a n d A M L based on immunophenotyping CD19

B-lineage T-lineage AML

CD7

+

CD33

CD13

-

-

+ /%"

__ +

+

HI,A-DR +

TdT + '

i, +

+

d

"(3)7 is identified in a small proportion of AML cases. I'HLA-DR is expressed in <10% of cases of T-ALL. 'TdT is negative in tile most mature B-lineage ALL (Smlg positiw~). 'JTdT has been identified in some cases of AMI,(M1). w h e r e a) t h e m o r p h o l o g y or c y t o c h e m i s t r y d o e s n o t c l e a r l y i d e n t i f y t h e l i n e a g e of l e u k e m i c cells, b) t h e r e m a y be m o r e t h a n o n e l i n e a g e of l e u k e m i c cells, a n d c) a m o r p h o l o g i c a l l y l y m p h o i d l e u k e m i a is f o u n d to lack e x p r e s s i o n of specific l y m p h o i d s u r f a c e a n t i g e n s . U s i n g a c o m b i n a t i o n of m o n o c l o n a l a n t i b o d i e s {Table 5), 9 0 % - 9 9 % of A M L s h o u l d be d i s c r i m i n a t e d f r o m ALL. T h e r e h a v e b e e n s e v e r a l a t t e m p t s to i d e n t i f y i m m u n o l o g i c a l l y - d e f i n e d s u b g r o u p s of A M L a n d to c o r r e l a t e t h e s e g r o u p s w i t h t h e FAB c l a s s i f i c a t i o n [19]. In g e n e r a l , p h e n o t y p e s s p e c i f i c for e a c h FAB c l a s s h a v e n o t b e e n i d e n t i f i e d , b u t c e r t a i n assoc i a t i o n s h a v e b e e n c o m m o n l y o b s e r v e d ( T a b l e 6). T h e m o s t s p e c i f i c p h e n o t y p e s are t h e a s s o c i a t i o n of M 4 / M 5 w i t h e x p r e s s i o n of t h e gp55 a n t i g e n (CD14) a n d t h e lack of e x p r e s s i o n of c l a s s II H L A a n t i g e n s (HLA-DR) in M3. M1 m a y b e d i f f e r e n t i a t e d f r o m M2 o n t h e b a s i s of Leu M1 r e a c t i v i t y , b e i n g n e g a t i v e i n M1 a n d p o s i t i v e i n M 2 [20]. F u r t h e r i m m u n o l o g i c a l d a t a s h o u l d be a c c u m u l a t e d i n o r d e r to d e t e r m i n e if i m m u n o l o g i c a l l y - d e f i n e d s u b g r o u p s of A M L h a v e d i f f e r e n t p r o g n o s e s a n d if t h e r e are s p e c i f i c p h e n o t y p e s a s s o c i a t e d w i t h s p e c i f i c c h r o m o s o m a l a b n o r m a l i t i e s .

Bilineage

and

Biphenotypic

Leukemias

B i l i n e a g e a n d b i p h e n o t y p i c l e u k e m i a s , i.e., l e u k e m i a s in w h i c h m a r k e r s of b o t h l y m p h o i d a n d m y e l o i d l i n e a g e s are e x p r e s s e d e i t h e r b y t w o or m o r e d i s t i n c t subp o p u l a t i o n s ( b i l i n e a g e l e u k e m i a s ) or c o e x p r e s s e d by t h e s a m e l e u k e m i c cells (bip h e n o t y p i c l e u k e m i a s ) a p p e a r to r e p r e s e n t u n i q u e c a t e g o r i e s of a c u t e l e u k e m i a t h a t are i d e n t i f i a b l e p r i m a r i l y b y i m m u n o l o g i c m e t h o d s . T h e d i a g n o s i s r e q u i r e s a n a l y s i s

Table 6

C o r r e l a t i o n of m e m b r a n e m a r k e r s w i t h FAB c l a s s i f i c a t i o n

Antibodies

M1

M2

HLA-DR CD34 CD33 CDI3 CDll CD'I5 CD 14 Glycophorin A Platelet GPIIb/IIIa/Ib (J15,AN51, C17)

+ + + +/

~ +/+ 4 Jr + +/

NR; not reported.

.

.

M3

+ + +/ +/ .

-

.

. -

M4

M5

M6

M7

+ +/+ + + + +

+ t/ ~ + + + +

+/ +/

+/ +/ +/NR NR NR NR

+/ +

+

13

MIC Classification of AML

Table 7

Lineage-restricted markers

Granulocytic

Monocytic

Erythroid

Megakaryocytic

Peroxidase CD34 CD] 3

ANAE _+F~ CD34 CD13 CD14

Glycophorin A Spectrin

Platelet glycoproteins IIb/IIIa/Ib/llIa

B cell Surface and/or cytoplasmic lg CD19 CD20

T cell CD5 CD3 CD2 ~' CD7 ~'

"Alpha naphthyl acetate esterase ÷ fluoride inhibition. hThese antigens have been identified on rare ANLL-AMLcells. with lineage-restricted markers (Table 7). Distinguishing bilineage and biphenotypic leukemias generally should involve a double staining procedure (dual fluorescence or c o m b i n e d cytochemistry and immunofluorescence). Although only small numbers of cases have been reported, therapy of these cases with standard ALL c h e m o t h e r a p y has been associated with a low complete remission rate and short survival. It is critical to identify and c o m p l e t e l y evaluate bilineage and biphenotypic leukemias p r o s p e c t i v e l y in all therapeutic trials in an effort to determine the actual incidence, to define a p p r o p r i a t e treatments, and to establish possible correlations with c h r o m o s o m e abnormalities. Bilineage and b i p h e n o t y p i c leukemias should be distinguished from m o r p h o l o g i c a l l y l y m p h o i d or undifferentiated leukemias (less than 3% peroxidase-positive blasts), w h i c h express m y e l o i d markers but lack l y m p h o i d markers. These cases should be classified as AML. MIC CLASSIFICATION OF AML

The MIC classification established ten subtypes of AML, w h i c h are characterized by unique cytogenetic, morphologic, and i m m u n o l o g i c a l criteria. All of these subtypes are presented schematically in Figures 1-10 of this report and a c c o m p a n i e d in each case by the MIC notation of the condition. DISCUSSION

The Second MIC Cooperative Study Group evaluated the cytogenetic changes found in the majority of the AML cases reported in recent series and based on high quality banding. Specific changes are found, often as single abnormalities, in about 60% of the cases with abnormal karyotypes. At present about 33% of the reported AML cases have not been shown to have clonal chromosomal abnormalities. However, this group of patients, i.e., those without detectable c h r o m o s o m a l changes in the bone marrow cells, may become less n u m e r o u s as cytogenetic techniques improve and their a p p l i c a t i o n is more widespread. At present it is i m p o s s i b l e to arrive at an accurate evaluation of prognostic factors (including survival) for the various subtypes of AML as defined here because of a n u m b e r of factors: a) an insufficient n u m b e r of cases in certain subtypes, b) lack of uniformity in the therapy of the patients, and c) missing important information in m a n y of the cases reported in the literature. However, there is a suggestion that certain c h r o m o s o m e abnormalities may be associated with a particular clinical outcome. For example, patients with M4Eo/inv(16) have been reported to have very high complete remission rate, those with m o n o s o m y 7 ( - 7 ) a poor prognosis, and patients with M3/t(15;17) a long duration of remissions. Within each

14

Second MIC Cooperative Study Group subtype of AML, the biology of the disease (and, thus, its clinical aspects i n c l u d i n g survival) is related to if not decided by the specific chromosome change. When additional karyotypic changes appear, the leukemia usually becomes more aggressive, with complex chromosomal abnormalities being associated with a short survival. Particularly complex karyotypes are encountered in M6 and, hence, this subtype of AML is usually associated with a poor prognosis. The presence or absence of cytogenetically normal cells also has a prognostic effect in addition to the other karyotypic facets. A recurring theme encountered by the MIC Group was the dichotomy between some of the specific chromosome changes between M2 and M4 [e.g., +4, +8, t(6;9)] and less frequently between M1 and M2 [t(9;22), inv(3)]. It is possible that in each case we may be dealing with only one subtype of AML as defined cytogenetically, with the cellular morphology s p a n n i n g a wide spectrum from that of myeloblastic nature to that of myelomonocytic in M2 and M4, and in M1 and M2 from less to more mature myeloblasts. Serious consideration may have to be given to the possibility that some of the subtypes of AML may be more accurately defined cytogenetically, than by other criteria, particularly when their morphologic aspects are inconsistent. Some of the chromosomal abnormalities may be associated with the presence of a myelodysplastic phase or aspect, e.g., 5 q - , - 7 , anomalies of chromosome #3, or t(6;9), and will be the subject of a future MIC Workshop. It is recoInmended that cooperative groups and i n d i v i d u a l clinicians pay particular attention to the relationship of specific chromosome abnormalities to the therapeutic response, survival, and other important parameters of each case of AML (iinmunology, cytochemistry, epidemiology) In this m a n n e r investigators will be in a position to arrive at more optimal and meaningful correlations between specific karyotypic changes and subtypes of AML, particularly those subtypes in which the n u m b e r of cases is at present relatively small.

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