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The incidence of hybrid acute leukaemias
Leukemia Research Vol. 12, No. 9, pp. 707-709, 1988.
0145--212(~/88 $3.00 + .00 Pergamon Press pie
Printed in Great Britain.
THE INCIDENCE OF HYBRID ACUTE LEUKAEMIAS GUILLERMO J. RUIZ-ARGUELLES,* EDUARDO LOBATO-MENDIZABAL*i" and ANTONIO MARfN-LOPEZi" *Laboratorios Clinicos de Puebla, *tCentro de Hematologia y Medicina Interna de Puebla and tHospital Universitario de Puebla, Puebla, Pue., Mrxico
(Received 10 March 1988. Accepted 30 May 1988) Abstract--During a 4-yr period, 292 patients with acute leukaemia were studied using morphology, cytochemistry and immunologic reagents to determine the cell lineage of the leukaemia. One hundred and sixty-three cases were shown to be acute lymphoblastic leukaemia (ALL), 127 acute myeloblastic leukaemia (AML) and two cases (0.6%) were classified as hybrid acute leukaemias. One was biphenotypic in which the blast cells displayed both T-lymphoid (60% E-rosettes) and megakaryocytic markers (47% CDw41/glycoprotein IIb/IIIa antigen, 50% myeloperoxidase). The second was a bilineal acute leukaemia in which some blast cells displayed B-lymphoid (47% CD10/CALLA, 40% acid phosphatase) features and other megakaryocytic (33% coagulation factor VIII:WVf antigen)/ myeloid (30% Sudan Black) features. This study suggests that hybrid acute leukaemia are rare.
Key words: Acute leukaemia, hybrid, bilineal, biphenotypic.
studied 292 patients with acute leukaemia and found two cases of HAL: one instance of biphenotypic H A L (T-lymphoblastic/megakaryoblastic) and one instance of bilineal H A L (Common-lymphoblastic/ megakaryoblastic).
INTRODUCTION NUMEROUS terms have been used to refer to acute leukaemias (AL) with both myeloid and lymphoid features: hybrid, mixed, biphenotypic, biclonal, bilineal, simultaneous, chimeric, and others. Gale and Ben Bassat [1] recently published criteria to both classify and name these malignancies. They propose the term hybrid acute leukaemias (HAL) for AL that demonstrate malignant transformation of both lymphoid and myeloid cells. When 10% or more of the malignant cells demonstrate both lymphoid and myeloid features they suggested the term biphenotypic HAL. When the leukemia cells are heterogeneous with single cells displaying either lymphoid or myeloid features but not both, they propose the term bilineal HAL. The diagnostic criteria for H A L have been also summarized in the paper by Gale and Ben Bassat [1]. Using these criteria, we prospectively
M A T E R I A L AND METHODS All patients with acute leukaemia studied and/or treated at Laboratorios Clinicosde Puebla, Centro de Hematologia y Medicina Interna de Puebla and Hospital Universitario de Puebla, Puebla, Mexico, entered this prospective study. The object was to classify their maliguancies using morphology, cytochemistry and immunologic markers; the latter included: E-rosette formation, cytoplasmic and surface immunoglobulin staining and reactivity with the following monoclonal antibodies: J5 (anti-CD10/CALLA antigen), HPI-ld (anti-CDw41/giycoprotein IIb/IIIa antigen), BMA-0200 (anti-CD15 antigen), Wl-23 (anticoagulation FVIII-VWf antigen), R2-3 (anti-transferrin receptor antigen) and R1-3 (anti-plasma cell antigen); all these reagents have been previously used to classify acute leukaemias [2-4]. Cytochemistry studies included myeloperoxidase, chloracetate esterase, Sudan black, and acid phosphatase; morphology was classified according to the FAB criteria
Abbreviations: AL, acute leukaemia; HAL, hybrid acute leukaemia; ALL, acute lymphoblastic leukaemia; AML, acute myeloblastic ieukaemia; CALLA, common acute lymphoblastic leukaemia antigen; Gp lib/Ilia, platelet glycoprotein IIb/IIIa; FVIII-VWf, coagulation factor VIII, Von Willebrand factor; FAB, French-American-British morphological classification of acute leukaemia. Correspondence to: Dr Guillermo J. Ruiz-Argiielles, Consultant in Haematology, Laboratorios Clinicos de Puebla, Diaz Ordaz 808, 72530 Puebla, Pue., Mexico.
[51. RESULTS One hundred and sixty-three of 292 patients were found to have acute lymphoblastic leukaemia (ALL) and 127, acute myeloblastic leukaemia (AML). 707
708
G. J. RUIZ-ARGOELLESet al. TABLE 1
Marker Lymphoid: a) Major E-rosettes Surface lg Cytoplasmic Ig b) Minor Acid phosphatase CALLA-J5 Myeloid a) Major Myeloperoxidase Auer rods (b) Minor Sudan black Hpl-ld W1-23 BMA-0200 Others R2-3 Morphology
Antigen
Patient 1
Patient 2
CD2 ---
60% 3% 0%
6% 0% 0%
-CD 10
10% 0%
40% 47 %
50% Negative
0% Negative
m
m
GPIIb/IIIa/CDw41 FVIII-VWf CD15
47% 2% 0%
30% 0% 33% 0%
Transf. receptor
3% L2
7% L2
--
0%
Lymphoid and myeloid markers of the two patients with hybrid acute leukaemia. According to Gale and Ben Bassat [1], one major and/or two minor markers are required to define lymphoid or myeloid lineage. CALLA: Common acute lymphoblastic leukaemia (CD10) antigen, identified by monoclonal antibody J5. GpIIb/IIIa: Glycoprotein IIb/IIIa (CDw41) antigen identified by monoclonal antibody HPI-ld. FVIII-VWf: Coagulation factor VIII-VWf antigen, identified by monoclonal antibody Wl-23. Transf. receptor: Transferrin receptor antigen identified by monoclonal antibody R2-3. Using the diagnostic criteria suggested by Gale and Ben Bassat [1] two cases of H A L were identified (0.6%); Table 1 shows features of the malignant cells of both cases. Case number 1 presented in a 40yr old male and was treated with weekly pulses of vincristine and prednisone. The patient died two weeks after the diagnosis was established from uncontrolled leukaemia. Case number 2 presented in a 32-year old male. He was treated with weekly pulses of adriamycin, vincristine and prednisone, but also died with uncontrolled leukaemia 4 months after the diagnosis. Haematologic remission was not achieved in either of the patients. Chromosomal studies in both cases showed no abnormality. DISCUSSION H A L is uncommon [1]. Using stringent criteria less than 40 cases have been published in the literature [1]. The prevalence of H A L is unknown inasmuch as these criteria have not been widely used to precisely define H A L . The less than 1% prevalence we have found supports the idea that H A L is infrequent. We did not investigate either immunoglobulin or T-cell
receptor gene rearrangements, so it is possible that we have underestimated instances of H A L . The prevalence of H A L has been found to be higher by other authors: Gonzalez et al. [6] using the same criteria as in this report found a prevalence of 1.5% for H A L in a group of 470 cases of AL, in Spain. The number of monoclonal antibodies used in our study is smaller than that employed by other authors and may explain in part the low prevalence of H A L in our series; however, the reactivity with monoclonal antibodies is only a minor criteria for the diagnosis of H A L [1]. Higher prevalences of H A L using less stringent criteria have been reported by other authors: Mirro et al. reported a 19% prevalence of H A L [7]; Stass and Mirro have estimated that approx. 25% of cases diagnosed as myeloid leukaemias will possess lymphoid-associated surface antigens, while 13% of those leukaemias that appear to be typical A L L will have surface markers common to the myeloid lineage [8]. The expression of myeloid related antigens in cases of adult A L L have been shown to identify a high-risk group of such patients [9]; however, the expression of such antigens is not sufficient to classify these malignancies as H A L [1].
Prevalence of hybrid acute leukaemia in Mexico Both of our cases of H A L had a megakaryocytic component as part of the myeloid lineage. Acute megakaryoblastic leukaemia or M7 variant of A M L [10], comprises 8% of all the cases of acute leukaemia in our series [2, 4, 11]. This is a higher prevalence than that found in some countries [12], but similar to that found in the United States [13, 14]. It is also of interest that although T - A L L is very infrequent in Mexico, comprising only 5.4% of A L L cases [3], one of our patients with H A L displayed T-cell markers (E-rosettes). We believe that racial a n d / o r geographical factors may account for the differences observed [15], so that H A L may have, in other places, different lymphoid or myeloid components. A n o t h e r factor that may also influence the prevalence of H A L in our study could be the referral patterns: most of the patients included in our study are residents of the southeast region of our country. Finally, the treatment outcome in both of our patients with H A L was poor, similar to that previously recorded [1]. It is concluded that the prevalence of H A L , using the stringent criteria proposed by Gale and Ben Bassat [1], is low in Puebla, Mexico as compared with that observed in other countries.
Acknowledgements--The authors are most grateful to Dr Robert Peter Gale for his careful and helpful criticism of the manuscript. Dr Alejandro Ruiz-Argiielles is acknowledged for the immunological studies of the malignant cells and his review of the paper. Monoclonal antibodies HPI-ld, W1-23 and R2-3 were a generous gift of Drs William L. Nichols, Jerry A. Katzmann and Nick J. Gonchoroff, respectively, from the Mayo Clinic. The Consejo Estatal de Ciencia y Technologia de Puebla provided the other immune reagents. The drugs used to treat the patients were supplied by the Asociacion Poblana de Apoyo a Personas con Problemas Onco-Hematologicos A.C.
REFERENCES 1. Gale R. P. & Ben Bassat I. (1987) Hybrid acute leukaemia (Annotation). Br. J. Haemat. 65, 261. 2. Ruiz-Argiielles G. J., Marin-L6pez A., Lobato-Mendizfibal E., Ruiz-Argiielles A., Nichols W. & Katzmann J. A. (1986) Acute megakaryoblastic leukaemia: a prospective study of its identification and treatment. Br. J. Haemat. 62, 55.
709
3. Ruiz-Argiielles G. J., Marin-L6pez A., Ruiz-Argiielles A., Valls-de-Ruiz M., Pdrez-Romano B. & Ruiz-Gonzalez O.S. (1987) Estudio prospectivo de la clasificaci6n inmunol6gica de 128 casos de leucemia aguda linfoblfistica en la ciudad de Puebla, Mdxico. Reota Invest. clin. Hosp. Enferm. Nutr., Mix. 39, 137. 4. Ruiz-Argiielles G. J., Marin-L6pez A. & Ruiz-Argiielles A. (1987) Immunologic classification of the acute non-granular leukemias in the city of Puebla, Mdxico: its value in the diagnosis and prognosis. Reota. Invest. clin. Hosp. Enferm. Nutr., M~x. 39, 143. 5. Bennet J. M., Catovsky D., Daniel M. T., Flandrin G, Galton D. A. G., Gralnick H. R. & Sultan C. (1976) Proposals for the classification of acute leukemia. Br. J. Haemat. 33, 451. 6. Gonz~ilez M., San Miguel J. F., Cafiizo M. G., Orfao A., Ojeda E. & L6pez-Borrasca A. (1987) Hybrid acute leukaemia. Br. J. Haemat. 67, 117 (letter). 7. Mirro J., Zipf T. F., Pui C. H., Kitchingman G., Williams D., Melvin S., Murphy S. B. & Stass S. (1985) Acute mixed lineage leukemia: clinicopathologic correlations and prognostic significance. Blood 66, 1115. 8. Stass S. A. & Mirro Jr J. (1986) Lineage heterogeneity in acute leukaemia: acute mixed-lineage leukaemia and lineage switch. Clin haemat. 15, 811. 9. Sobol R. E., Mick R., Roston I., Davey F. R., Ellison R. R., Newman R., Cuttner J., Griffin J. D., Collins H., Nelson D. A. & Bloomfield C. D. (1987) Clinical importance of myeloid antigen expression in adult acute lymphoblastic leukemia. New Engl. J. Med. 316, 1111. 10. Bennet J. M., Catovsky D., Daniel M. T., Flandrin G., Galton D. A. G., Gralnick H. R. & Sultan C. (1985) Criteria for the diagnosis of acute leukaemia of megakaryocytic lineage (M7). Ann. intern. Med. 103, 450. 11. Ruiz-ArgiieUes G. J., Marin-L6pez A., Ruiz-Gonzales D. S. & Pdrez-Romano B. (1988) A prospective trial of the treatment of acute megakaryoblastic leukaemia. Clin. Lab. Haemat. 10, 15. 12. Cafiizo M. C., San Miguel J. F., Gonz~ilez M., Anta J. P., Offao A. & L6pez-Borrasca A. (1987) Discrepancies between morphologic, cytochemical and immunologic characteristics in acute myeloblastic leukemia. Am. J. clin. Path. 88, 38. 13. Huang M. J., Li C. Y., Nichols W. L., Young J. H. & Katzmann J. A. (1984) Acute leukemia with megakaryocytic differentiation: a study of twelve cases identified immunocytochemicaUy. Blood 64, 427. 14. Peterson B. A. & Levine E. G. (1987) Uncommon subtypes of acute nonlymphoblastic leukemia: clinical features and management of FAB M5, M6 and M7. Sem. Oncol. 14, 425. 15. S~inchez-Medal L. & Ruiz-Reyes G. (1987) Peculiarities of hematology in Latin America. In Oxford Textbook of Medicine (Weatherall D. J., Ledingham J. G. G. & Warrell D. A. Eds), 2nd Edn., Vol. II, pp. 19.268. Oxford Medical Publications, Oxford.
0145--212(~/88 $3.00 + .00 Pergamon Press pie
Printed in Great Britain.
THE INCIDENCE OF HYBRID ACUTE LEUKAEMIAS GUILLERMO J. RUIZ-ARGUELLES,* EDUARDO LOBATO-MENDIZABAL*i" and ANTONIO MARfN-LOPEZi" *Laboratorios Clinicos de Puebla, *tCentro de Hematologia y Medicina Interna de Puebla and tHospital Universitario de Puebla, Puebla, Pue., Mrxico
(Received 10 March 1988. Accepted 30 May 1988) Abstract--During a 4-yr period, 292 patients with acute leukaemia were studied using morphology, cytochemistry and immunologic reagents to determine the cell lineage of the leukaemia. One hundred and sixty-three cases were shown to be acute lymphoblastic leukaemia (ALL), 127 acute myeloblastic leukaemia (AML) and two cases (0.6%) were classified as hybrid acute leukaemias. One was biphenotypic in which the blast cells displayed both T-lymphoid (60% E-rosettes) and megakaryocytic markers (47% CDw41/glycoprotein IIb/IIIa antigen, 50% myeloperoxidase). The second was a bilineal acute leukaemia in which some blast cells displayed B-lymphoid (47% CD10/CALLA, 40% acid phosphatase) features and other megakaryocytic (33% coagulation factor VIII:WVf antigen)/ myeloid (30% Sudan Black) features. This study suggests that hybrid acute leukaemia are rare.
Key words: Acute leukaemia, hybrid, bilineal, biphenotypic.
studied 292 patients with acute leukaemia and found two cases of HAL: one instance of biphenotypic H A L (T-lymphoblastic/megakaryoblastic) and one instance of bilineal H A L (Common-lymphoblastic/ megakaryoblastic).
INTRODUCTION NUMEROUS terms have been used to refer to acute leukaemias (AL) with both myeloid and lymphoid features: hybrid, mixed, biphenotypic, biclonal, bilineal, simultaneous, chimeric, and others. Gale and Ben Bassat [1] recently published criteria to both classify and name these malignancies. They propose the term hybrid acute leukaemias (HAL) for AL that demonstrate malignant transformation of both lymphoid and myeloid cells. When 10% or more of the malignant cells demonstrate both lymphoid and myeloid features they suggested the term biphenotypic HAL. When the leukemia cells are heterogeneous with single cells displaying either lymphoid or myeloid features but not both, they propose the term bilineal HAL. The diagnostic criteria for H A L have been also summarized in the paper by Gale and Ben Bassat [1]. Using these criteria, we prospectively
M A T E R I A L AND METHODS All patients with acute leukaemia studied and/or treated at Laboratorios Clinicosde Puebla, Centro de Hematologia y Medicina Interna de Puebla and Hospital Universitario de Puebla, Puebla, Mexico, entered this prospective study. The object was to classify their maliguancies using morphology, cytochemistry and immunologic markers; the latter included: E-rosette formation, cytoplasmic and surface immunoglobulin staining and reactivity with the following monoclonal antibodies: J5 (anti-CD10/CALLA antigen), HPI-ld (anti-CDw41/giycoprotein IIb/IIIa antigen), BMA-0200 (anti-CD15 antigen), Wl-23 (anticoagulation FVIII-VWf antigen), R2-3 (anti-transferrin receptor antigen) and R1-3 (anti-plasma cell antigen); all these reagents have been previously used to classify acute leukaemias [2-4]. Cytochemistry studies included myeloperoxidase, chloracetate esterase, Sudan black, and acid phosphatase; morphology was classified according to the FAB criteria
Abbreviations: AL, acute leukaemia; HAL, hybrid acute leukaemia; ALL, acute lymphoblastic leukaemia; AML, acute myeloblastic ieukaemia; CALLA, common acute lymphoblastic leukaemia antigen; Gp lib/Ilia, platelet glycoprotein IIb/IIIa; FVIII-VWf, coagulation factor VIII, Von Willebrand factor; FAB, French-American-British morphological classification of acute leukaemia. Correspondence to: Dr Guillermo J. Ruiz-Argiielles, Consultant in Haematology, Laboratorios Clinicos de Puebla, Diaz Ordaz 808, 72530 Puebla, Pue., Mexico.
[51. RESULTS One hundred and sixty-three of 292 patients were found to have acute lymphoblastic leukaemia (ALL) and 127, acute myeloblastic leukaemia (AML). 707
708
G. J. RUIZ-ARGOELLESet al. TABLE 1
Marker Lymphoid: a) Major E-rosettes Surface lg Cytoplasmic Ig b) Minor Acid phosphatase CALLA-J5 Myeloid a) Major Myeloperoxidase Auer rods (b) Minor Sudan black Hpl-ld W1-23 BMA-0200 Others R2-3 Morphology
Antigen
Patient 1
Patient 2
CD2 ---
60% 3% 0%
6% 0% 0%
-CD 10
10% 0%
40% 47 %
50% Negative
0% Negative
m
m
GPIIb/IIIa/CDw41 FVIII-VWf CD15
47% 2% 0%
30% 0% 33% 0%
Transf. receptor
3% L2
7% L2
--
0%
Lymphoid and myeloid markers of the two patients with hybrid acute leukaemia. According to Gale and Ben Bassat [1], one major and/or two minor markers are required to define lymphoid or myeloid lineage. CALLA: Common acute lymphoblastic leukaemia (CD10) antigen, identified by monoclonal antibody J5. GpIIb/IIIa: Glycoprotein IIb/IIIa (CDw41) antigen identified by monoclonal antibody HPI-ld. FVIII-VWf: Coagulation factor VIII-VWf antigen, identified by monoclonal antibody Wl-23. Transf. receptor: Transferrin receptor antigen identified by monoclonal antibody R2-3. Using the diagnostic criteria suggested by Gale and Ben Bassat [1] two cases of H A L were identified (0.6%); Table 1 shows features of the malignant cells of both cases. Case number 1 presented in a 40yr old male and was treated with weekly pulses of vincristine and prednisone. The patient died two weeks after the diagnosis was established from uncontrolled leukaemia. Case number 2 presented in a 32-year old male. He was treated with weekly pulses of adriamycin, vincristine and prednisone, but also died with uncontrolled leukaemia 4 months after the diagnosis. Haematologic remission was not achieved in either of the patients. Chromosomal studies in both cases showed no abnormality. DISCUSSION H A L is uncommon [1]. Using stringent criteria less than 40 cases have been published in the literature [1]. The prevalence of H A L is unknown inasmuch as these criteria have not been widely used to precisely define H A L . The less than 1% prevalence we have found supports the idea that H A L is infrequent. We did not investigate either immunoglobulin or T-cell
receptor gene rearrangements, so it is possible that we have underestimated instances of H A L . The prevalence of H A L has been found to be higher by other authors: Gonzalez et al. [6] using the same criteria as in this report found a prevalence of 1.5% for H A L in a group of 470 cases of AL, in Spain. The number of monoclonal antibodies used in our study is smaller than that employed by other authors and may explain in part the low prevalence of H A L in our series; however, the reactivity with monoclonal antibodies is only a minor criteria for the diagnosis of H A L [1]. Higher prevalences of H A L using less stringent criteria have been reported by other authors: Mirro et al. reported a 19% prevalence of H A L [7]; Stass and Mirro have estimated that approx. 25% of cases diagnosed as myeloid leukaemias will possess lymphoid-associated surface antigens, while 13% of those leukaemias that appear to be typical A L L will have surface markers common to the myeloid lineage [8]. The expression of myeloid related antigens in cases of adult A L L have been shown to identify a high-risk group of such patients [9]; however, the expression of such antigens is not sufficient to classify these malignancies as H A L [1].
Prevalence of hybrid acute leukaemia in Mexico Both of our cases of H A L had a megakaryocytic component as part of the myeloid lineage. Acute megakaryoblastic leukaemia or M7 variant of A M L [10], comprises 8% of all the cases of acute leukaemia in our series [2, 4, 11]. This is a higher prevalence than that found in some countries [12], but similar to that found in the United States [13, 14]. It is also of interest that although T - A L L is very infrequent in Mexico, comprising only 5.4% of A L L cases [3], one of our patients with H A L displayed T-cell markers (E-rosettes). We believe that racial a n d / o r geographical factors may account for the differences observed [15], so that H A L may have, in other places, different lymphoid or myeloid components. A n o t h e r factor that may also influence the prevalence of H A L in our study could be the referral patterns: most of the patients included in our study are residents of the southeast region of our country. Finally, the treatment outcome in both of our patients with H A L was poor, similar to that previously recorded [1]. It is concluded that the prevalence of H A L , using the stringent criteria proposed by Gale and Ben Bassat [1], is low in Puebla, Mexico as compared with that observed in other countries.
Acknowledgements--The authors are most grateful to Dr Robert Peter Gale for his careful and helpful criticism of the manuscript. Dr Alejandro Ruiz-Argiielles is acknowledged for the immunological studies of the malignant cells and his review of the paper. Monoclonal antibodies HPI-ld, W1-23 and R2-3 were a generous gift of Drs William L. Nichols, Jerry A. Katzmann and Nick J. Gonchoroff, respectively, from the Mayo Clinic. The Consejo Estatal de Ciencia y Technologia de Puebla provided the other immune reagents. The drugs used to treat the patients were supplied by the Asociacion Poblana de Apoyo a Personas con Problemas Onco-Hematologicos A.C.
REFERENCES 1. Gale R. P. & Ben Bassat I. (1987) Hybrid acute leukaemia (Annotation). Br. J. Haemat. 65, 261. 2. Ruiz-Argiielles G. J., Marin-L6pez A., Lobato-Mendizfibal E., Ruiz-Argiielles A., Nichols W. & Katzmann J. A. (1986) Acute megakaryoblastic leukaemia: a prospective study of its identification and treatment. Br. J. Haemat. 62, 55.
709
3. Ruiz-Argiielles G. J., Marin-L6pez A., Ruiz-Argiielles A., Valls-de-Ruiz M., Pdrez-Romano B. & Ruiz-Gonzalez O.S. (1987) Estudio prospectivo de la clasificaci6n inmunol6gica de 128 casos de leucemia aguda linfoblfistica en la ciudad de Puebla, Mdxico. Reota Invest. clin. Hosp. Enferm. Nutr., Mix. 39, 137. 4. Ruiz-Argiielles G. J., Marin-L6pez A. & Ruiz-Argiielles A. (1987) Immunologic classification of the acute non-granular leukemias in the city of Puebla, Mdxico: its value in the diagnosis and prognosis. Reota. Invest. clin. Hosp. Enferm. Nutr., M~x. 39, 143. 5. Bennet J. M., Catovsky D., Daniel M. T., Flandrin G, Galton D. A. G., Gralnick H. R. & Sultan C. (1976) Proposals for the classification of acute leukemia. Br. J. Haemat. 33, 451. 6. Gonz~ilez M., San Miguel J. F., Cafiizo M. G., Orfao A., Ojeda E. & L6pez-Borrasca A. (1987) Hybrid acute leukaemia. Br. J. Haemat. 67, 117 (letter). 7. Mirro J., Zipf T. F., Pui C. H., Kitchingman G., Williams D., Melvin S., Murphy S. B. & Stass S. (1985) Acute mixed lineage leukemia: clinicopathologic correlations and prognostic significance. Blood 66, 1115. 8. Stass S. A. & Mirro Jr J. (1986) Lineage heterogeneity in acute leukaemia: acute mixed-lineage leukaemia and lineage switch. Clin haemat. 15, 811. 9. Sobol R. E., Mick R., Roston I., Davey F. R., Ellison R. R., Newman R., Cuttner J., Griffin J. D., Collins H., Nelson D. A. & Bloomfield C. D. (1987) Clinical importance of myeloid antigen expression in adult acute lymphoblastic leukemia. New Engl. J. Med. 316, 1111. 10. Bennet J. M., Catovsky D., Daniel M. T., Flandrin G., Galton D. A. G., Gralnick H. R. & Sultan C. (1985) Criteria for the diagnosis of acute leukaemia of megakaryocytic lineage (M7). Ann. intern. Med. 103, 450. 11. Ruiz-ArgiieUes G. J., Marin-L6pez A., Ruiz-Gonzales D. S. & Pdrez-Romano B. (1988) A prospective trial of the treatment of acute megakaryoblastic leukaemia. Clin. Lab. Haemat. 10, 15. 12. Cafiizo M. C., San Miguel J. F., Gonz~ilez M., Anta J. P., Offao A. & L6pez-Borrasca A. (1987) Discrepancies between morphologic, cytochemical and immunologic characteristics in acute myeloblastic leukemia. Am. J. clin. Path. 88, 38. 13. Huang M. J., Li C. Y., Nichols W. L., Young J. H. & Katzmann J. A. (1984) Acute leukemia with megakaryocytic differentiation: a study of twelve cases identified immunocytochemicaUy. Blood 64, 427. 14. Peterson B. A. & Levine E. G. (1987) Uncommon subtypes of acute nonlymphoblastic leukemia: clinical features and management of FAB M5, M6 and M7. Sem. Oncol. 14, 425. 15. S~inchez-Medal L. & Ruiz-Reyes G. (1987) Peculiarities of hematology in Latin America. In Oxford Textbook of Medicine (Weatherall D. J., Ledingham J. G. G. & Warrell D. A. Eds), 2nd Edn., Vol. II, pp. 19.268. Oxford Medical Publications, Oxford.