Epigenetic inactivation of INK4/CDK/RB cell cycle pathway in acute leukemias

Dysregulation of cell cycle is important in oncogenesis. We analyzed the inactivation of the INK4 family CKI/CDK/RB pathway by gene promoter hypermethylation in leukemogenesis. The methylation-specific polymerase chain reaction (MSP) with primers for methylated (M-MSP) and unmethylated (U-MSP) alleles of the p15, p16, p18, and RB genes was used to study five leukemic cell lines, 50 acute myeloid leukemia (AML) and 25 acute lymphoblastic leukemia (ALL) samples. None of the leukemic cell lines showed p18 and RB methylation. p15 was methylated in Raji, while p16 was methylated in U937 and Raji. In NB4 and Jurkat, both alleles of p15 and p16 appeared to be deleted. At diagnosis, p15 methylation occurred in 29 (58%) AML patients, and 10 (40.0%) ALL patients. p16 methylation occurred in two (4%) AML and two (8%) ALL patients. Only one each of AML and ALL patients had concurrent p15 and p16 methylation. None of the patients had methylation of p18 or RB. In AML, p15 methylation was associated with M2 subtype (p=0.018). Patients with and without p15 methylation had similar complete remission (CR) rates and projected 5-year overall survival (OS) or disease-free survival (DFS). Therefore, methylation inactivation of the INK4/CDK/RB pathway in leukemia involved primarily p15 and occasionally p16, but not p18 or RB. In AML, p15 gene methylation was associated with the M2 subtype, but was not prognostic for CR, OS, or DFS.     

Expression of the Fas antigen on primary human leukemia cells

Summary The antigen defined by the monoclonal antibody anti-Fas can mediate apoptosis, is associated with the receptor for tumor necrosis factor, and is expressed on a limited number of human tissues. In this study we analyzed the expression of Fas on primary human leukemic cells and on mononuclear cells from other hematologic disorders. A total of 95 samples of blood or bone marrow were studied by indirect immunofluorescence. These samples included the normal controls, 47 cases of acute myelogenous leukemia (AML), 11 cases of acute lymphoblastic leukemia (ALL), 21 cases of leukemic lymphoma, seven cases of chronic myelogenous leukemia (CML), five cases of plasma cell leukemia or multiple myeloma, and five cases of myelodysplastic or myeloproliferative syndromes. Normal controls were negative without exception. Among AML, 13/47 cases (28%) were positive; among ALL, 1/11 cases (9%) was positive; among leukemic lymphomas, 3/21 cases (14%) were positive. In a case of plasma cell leukemia which strongly expressed the Fas antigen, we demonstrated that the antibody mediates cell lysis, which was synergistically enhanced by the addition of rabbit complement. In patients with AML, Fas positivity had no obvious clinical relevance. Taken together, our results show that approximately 30% of cases of AML and occasionally other leukemias express the Fas antigens, whereas normal controls are negative in our test system. These findings may be useful in the treatment of refractory leukemias or may permit the purging of autologous transplants.Presented in part at the 34th annual meeting of the American Society of Hematology, Anaheim, CA, December 1992     

Leukemia-associated antigens in ALL.

A cytotoxic common ALL antiserum (CALLA) specific for leukemic cells of most patients with non-T-cel- acute lymphoblastic leukemia (ALL) and of some patients with chronic myelogenous leukemia (CML) in blast crisis has been reproducibly prepared using cell lines for absorption. CALLA reacts with leukemic cells of 110 of 134 patients (82%) with non-T-cell ALL; 1 of 71 (1%) patients with acute myelogenous leukemia (AML); 2 of 7 patients (29%) with chronic myelogenous leukemia in blast crisis; 7 of 92 patients (8%) with other hematologic malignancies; and with the leukemic cell lines Laz 221 and NALM-1. It does not react with the normal hematopoietic cells, B- or T-cell lines, or cells from 26 patients with T-cell ALL that were tested. CALLA reactivity and periodic acid Schiff (PAS) staining correlate poorly, with CALLA reacting with cells from 86% (64 of 74) of patients with PAS-positive and 76% (29 of 38) of those with PAS-negative non-T-cell ALL. In these patients, CALLA reacts with cells from 89% of those under age 12 (78 of 88); 74% of those aged 12--20 (20 of 27); and 58% of those over 20 (11 of 19). Using only CALLA and antisera specific for Ia-like and T-cell antigens, we can now distinguish most cases of ALL from AML and other hematologic malignancies.     

Demonstration of antibodies binding to autologous and allogeneic leukemic cells in childhood ALL

Summary The humoral immune response to autologous leukemic cells was investigated in childhood ALL using a ¹²⁵I protein A binding assay. In 5/7 patients antibodies were demonstrated at diagnosis and in 3/7 cases also after chemotherapy. Sera from 2/3 patients, which bound significantly to autologous leukemic cells, did not bind significantly to autologous remission cells. In allogeneic experiments sera bound significantly to ALL leukemic cells (6/7 positive combinations), but not to AML leukemic cells (8/8 negative combinations). We propose that ALL sera contain antibodies binding to autologous leukemic cells and that they are directed against a common ALL antigen(s).Abbreviations ALL acute lymphoblastic leukemia - AML acute myeloid leukemia - CALLA common ALL antigen - CPM counts per minute - HTLV 1 human T cell leukemia/lymphoma virus, type 1 - I a immune-associated antigens - SE standard error     

Serial studies of bone marrow-derived fibroblastoid colony-forming cells and granulocyte/macrophage precursor cells in patients with acute leukemia

Bone marrow-derived fibroblastoid colony-forming cells (CFU-F) and granulocyte/macrophage precursor cells (CFU-GM) were studied in patients with acute leukemia. The numbers of CFU-F and CFU-GM were significantly lower in patients with acute myelogenous leukemia (AML) and acute lymphocytic leukemia (ALL) at diagnosis than in normal subjects, although patients with AML had a very wide range of CFU-F colony-forming efficiency. However, a suppressive effect of leukemic cells on normal CFU-F colony formation was not observed. CFU-F and CFU-GM in patients with acute leukemia recovered to normal levels when complete remission (CR) was achieved and decreased again at relapse. Serial studies showed that the increase in CFU-F preceded the recovery of CFU-GM. In AML, furthermore, patients who achieved CR had a higher number of CFU-F than patients without CR, suggesting that the CFU-F level at diagnosis may contribute to the prediction of the likelihood of remission induction in patients with AML.     

Detection of immunoglobulin gene rearrangement in acute and chronic lymphoid leukemias of B-cell lineage by polymerase chain reaction gene amplification

Polymerase chain reaction (PCR) was used to amplify the DNA fragments of the complementarity determining region 3 of the immunoglobulin (Ig) gene heavy chain from the leukemic cell specimens of patients with acute and chronic lymphoid leukemias of B-cell lineage. Two different pairs of primers were tested. Fourteen of the 17 (82%) cases of acute lymphoblastic leukemia (ALL), and all 15 cases (100%) of B-cell chronic lymphocytic leukemia, who had rearrangement of the Ig gene heavy chain by Southern analysis, were positive by PCR with either one or both pairs of primers. This technique was able to detect leukemic cells at the level of 0.1%. Applying it to study the remission marrow specimens following induction chemotherapy was more useful than morphology alone in predicting early relapse of the leukemia.     

Terminal deoxynucleotidyl transferase-positive acute myeloblastic leukemia

Terminal deoxynucleotidyl transferase (TdT) is a biochemical marker for acute lymphoblastic leukemia (ALL). In studies of ALL at diagnosis, there are usually greater than 40% TdT-positive cells by indirect immunofluorescence, whereas acute myeloblastic leukemia (AML) shows less than 1% TdT-positive cells. Rare cases of TdT-positive AML have been reported. We present here three AML patients with TdT in 15%, 45%, and 90% of the leukemic blasts. The diagnosis of AML was established on the basis of morphology and cytochemistry, and the cases included one patient with Auer rods. Myeloperoxidase was present respectively in 20%, 90%, and 5% of the blasts. There was no Philadelphia chromosome present in the three cases. These results may indicate the simultaneous presence of lymphoid and myeloid populations, or the presence of a blast cell with both lymphoid and myeloid markers.     

Effects of low dose Ara-C regimen in acute leukemias and RAEB

Recent increase of leukemia among elderly patients prompted us to investigate the types of leukemia which can be induced into remission by low-dose Ara-C (LDAC) regimen. LDAC regimen was performed in 30 cases with overt acute leukemia (A), hypoplastic leukemia (B), and RAEB (C); Group A consists of M1 (1 case), M2 (4 cases), M3 (1 case), M4 (4 cases), M6 (1 case), and ALL (2 cases), Group B AML (8 cases), ALL (2 cases), and null (1 case), Group C RAEB (2 cases), and RAEB-T (4 cases). Complete remission (CR) rate was 23% (3/13) in group A, 64% (7/11) in group B, 0% (0/6) in group C. Partial remission rate was 33% (2/6) in group C. In group A, patients with M2 were induced into CR. In group B, both AML and ALL were induced into CR. Hypocellular marrow indicating low leukemic burden related to good sensitivity to Ara-C. Duration of CR was rather short; mean duration being 5.3 months. In group C, 2 PR cases of RAEB showed partial hematological recovery. LDAC regimen is effective especially for most of hypoplastic leukemia and some of M2. Side effects were tolerable, but all CR cases passed through bone marrow hypoplasia and needed supportive cares.     

以降钙素基因高度甲基化为分子基因标志检测白血病微量残留病

目的 探讨以降钙素（CT）基因高度甲基化为白血病克隆的分子基因标志,检测白血病微量残留病（MRD）,并预测预后的可能性。方法 用限制性内切酶消化DNA〈应用聚合酶链反应（PCR）技术检测载9例急性白血病（AL）,其中急性淋巴细胞白血病（ALL）14例,急性非淋巴细胞白血病（ANLL）15例和8例慢性粒细胞白血病（CML）急变患者的CT基因的甲基化程度,对CT基因高度甲基化阳性者,以CT基因高度甲基化为白血病克隆的分子基因标志,应用PCR技术定期追踪检测骨髓MRD。结果 ALL中CT基因高度甲基化阳性率为857%（12/14）,ANLL为60%（9/15）,CML急变为100%（8/8）,而对照组无一例阳性,20例AL和CML急变患者完全缓解（CR）后均存在MRD,CR后MRD持续阳性或转阴后再次出现阳性,提示将发生骨髓复发,能提早2-11个月预示疾病的复发,MRD较早转阴并持续长期阴性者可能获得长期自下而上度。结论 以CT基因高度甲基化为白血病克隆的分子基因标志,应用PCR技术能起到监测白血病MRD的作用。为预测白血病的预后开辟了一条新途径。     

血液肿瘤患者FLT3/ITD基因突变的检测及临床意义

目的检测血液肿瘤患者FLT3/ITD基因突变,探讨其突变的临床意义。方法2001—2005年对南方医科大学南方医院血液科332例血液肿瘤患者,采用聚合酶链反应(PCR)方法检测FLT3/ITD基因突变。结果FLT3/ITD基因突变阳性率分别为急性髓性白血病(AML)22.3%(23/103)、慢性髓性白血病急变期(CML-BC)6.5%(2/31)、骨髓增生异常综合征(MDS)5.6%(2/36)和急性淋巴细胞白血病(ALL)2.6%(2/76)。而慢性髓性白血病慢性期(CML-CP)、慢性淋巴细胞白血病(CLL)、多发性骨髓瘤(MM)和非霍奇金淋巴瘤(NHL)均未发现FLT3/ITD基因突变。FLT3/ITD基因突变阳性AML患者外周血WBC计数及骨髓白血病细胞比例显著高于FLT3/ITD基因突变阴性AML患者(P<0.05),FLT3/ITD基因突变阳性AML患者完全缓解后18个月内累计复发率(63.6%)显著高于FLT3/ITD基因突变阴性AML组(27.7%)(P<0.05)。结论FLT3/ITD基因突变检测对血液肿瘤预后有一定意义;FLT3/ITD基因突变AML患者预后差。     

T cell acute lymphoblastic leukemia (T-ALL): New insights into the cellular origins and infiltration mechanisms common and unique among hematologic malignancies

T-cell acute lymphoblastic leukemia (T-ALL) accounts for 15% and 25% of total childhood and adult ALL cases, respectively. During T-ALL, patients are at risk of organ infiltration by leukemic T-cells. Infiltration is a major consequence of disease relapse and correlates with poor prognosis. Transendothelial migration of leukemic cells is required to exit the blood stream into target organs. While mechanisms of normal T-cell transmigration are well known, the mechanisms of leukemic T-cell extravasation remain elusive; but involvement of chemokines, integrins and Notch signaling play critical roles. Here, we summarize current knowledge about molecular mechanisms of leukemic T-cell infiltration with special emphasis on the newly identified subtype early T-cell-progenitor (ETP)-ALL. Furthermore, we compare the extravasation potential of T-ALL cells with that of other hematologic malignancies such as B-ALL and acute myeloid leukemia (AML).     

Growth of normal versus leukemic bone marrow cells in long term culture from acute lymphoblastic and myeloblastic leukemias

Summary The ability of the in vitro long-term bone marrow culture (LTBMC) system to impair the survival of leukemic cells and to enhance the growth of normal progenitors has been studied. Bone marrow cells from 19 acute lymphoblastic leukemia (ALL) and 30 acute myeloid leukemia (AML) patients at diagnosis were grown in LTBMC for 4–10 weeks. In half of the cases the leukemic population declined down to undetectable levels and was replaced by putative normal hemopoietic precursors, both in ALL and in AML. In the remaining cases, leukemic cells persisted throughout the culture time and few if any normal hemopoietic cells were detected. These data led us to extend to the lymphoid compartment the previous observation of decreasing leukemic myeloid blasts in LTBMC. The potential of such cultures as an in vitro purging system for autologous bone marrow transplantation in selected poor-prognosis lymphoid malignancies should be explored, as has been done for acute and chronic myeloid leukemias.     

Bone marrow necrosis in acute leukemia: Clinical characteristic and outcome

Bone marrow necrosis (BMN) is characterized by infarction of the medullary stroma, leading to marrow necrosis with preserved cortical bone. In reported small series, BMN in hematological malignancies is associated with poor prognosis. We sought to find the impact of BMN on clinical outcome in a relatively larger cohort of patients with acute leukemias. Overall we evaluated 1,691 patients; 1,051 with acute myeloid leukemia (AML) and 640 with acute lymphocytic leukemia referred to our institution between 2002 and 2013. Patients with AML and acute lymphoblastic leukemia (ALL) were evaluated separately to determine the incidence of BMN, associated clinical features and its prognostic significance. At initial diagnosis, BMN was observed in 25 (2.4%) patients with AML and 20 (3.2%) patients with ALL. In AML, BMN was significantly associated with French–American–British AML M5 morphology (32% vs. 10%, P = 0.002). The complete remission (CR) rate in AML with and without BMN was 32% and 59% respectively (P = 0.008). Likewise, CR rate in ALL with BMN was also inferior, 70% vs. 92% (P = 0.005). The median overall survival (OS) in AML with BMN was significantly poorer, 3.7 months compared to 14 months without BMN (P = 0.003). Similarly, the median OS in ALL with and without BMN was 61.7 and 72 months respectively (P = 0.33). BMN is not a rare entity in AML and ALL, but is infrequent. BMN in AML and in ALL is suggestive of inferior response and poor prognosis. Am. J. Hematol. 90:769–773, 2015. © 2015 Wiley Periodicals, Inc.     

P-glycoprotein (P-170) expression in acute leukemias

Multidrug resistance (MDR) is still a major obstacle to chemotherapy success in acute myeloid leukemia (AML) and to a less extent acute lymphoblastic leukemia (ALL). Recent studies have shown that the expression of certain gene products mediate the development of resistance to chemotherapeutic agents. The most well characterized of these genes is the multidrug resistance gene MDR-1. This study was planned to study the expression of P-glycoprotein/170 in patients with acute leukemia and the effect of Cyclosporin A (CSA) as a modulator of P-glycoprotein functional activity. The study was carried out on 20 patients with acute leukemia (14 AML cases and 6 ALL cases). In addition, 6 normal individuals served as a reference group. Flow cytometric analysis of P-gp/170 surface expression was performed using UIC-2 MoAb together with the functional assay using Rhodamine 123 (Rh 123) and Cyclosporin A as a modulator.P-gp/170 was expressed on the leukemic cells of 37.5% of relapsed patients (40.0% of AML and 33.3% of ALL cases), whereas 27.2% of de novo patients expressed P-gp/170 (33.3% of AML cases and 0% of ALL cases). The functional activity of MDR-1 gp was 71.4% in AML and 33.3% in ALL patients compared with16.6% in normal lymphocytes. From this study, it is clear that P-gp/170 is expressed to a higher degree in leukemic cells and this is greater in relapsed compared to de novo cases and more in AML than ALL blasts. Functional activity is a more sensitive predictor of chemoresistance than P-gp/170 surface expression.     

Aberrant methylation of DAP-kinase in therapy-related acute myeloid leukemia and myelodysplastic syndromes

Death-associated protein kinase (DAP-kinase), a proapoptotic serine/threonine kinase, is a candidate tumor suppressor gene. We studied the methylation status of DAP-kinase of 194 bone marrow samples from 160 patients with acute myeloid leukemia (AML) and 34 with a myelodysplastic syndrome (MDS) at the time of initial diagnosis by polymerase chain reaction (PCR). Hypermethylation of DAP-kinase was present in 27.5% (44 of 160) of AML and in 47% (16 of 34) of MDS specimens and significantly correlated to loss of DAP-kinase expression (P =.008). It was significantly more frequent in AML secondary to therapy for other malignancies (s-AML; 14 of 29, 48.3%), as compared to de novo AML (30 of 131, 22.9%, P =.01). DAP-kinase hypermethylation in AML was associated with myelodysplastic changes in the bone marrow at the time of the initial diagnosis (P =.002) and with the presence of cytogenetic abnormalities (P =.02). Alteration in the apoptotic response due to the loss of DAP-kinase function may be an early event in the transformation pathway to secondary leukemia via myelodysplasia.     

Lineage conversion from acute lymphoblastic leukemia to acute myeloid leukemia on rearrangement of the IgH gene in a patient with Down syndrome

A patient with Down syndrome (DS) at the time of diagnosis of acute lymphoblastic leukemia (ALL) had a relapse with acute myeloid leukemia (AML) after 4 years of complete remission. Although the diagnosis was AML, the leukemic blasts at relapse showed an immunoglobulin H rearrangement that turned out to be identical to that of the initial ALL blasts. It is thought that the leukemic precursor cells of this patient had the potential to differentiate into both lymphoid and myeloid lineages. This case is important for investigating target cells for leukemogenesis in DS.     

Epigenetic inactivation of the CIP/KIP cell-cycle control pathway in acute leukemias

Dysregulation of the cell cycle is important in oncogenesis. We analyzed the potential inactivation of the CIP/KIP family of the cyclin E/CDK/RB pathway by gene promoter hypermethylation in leukemias. The methylation-specific polymerase chain reaction (MSP) with primers for methylated (M-MSP) and unmethylated (U-MSP) alleles of the p21, p27, and p57 genes was used to study five leukemic cell lines, 50 acute myeloid leukemia (AML) samples, and 25 acute lymphoblastic leukemia (ALL) samples. p21 was hemizygously methylated in Raji and Jurkat but remained unmethylated in U937, HL60, and NB4. p27 was hemizygously methylated in Raji but unmethylated in the other cell lines. p57 was completely methylated in Raji and NB4, hemizygously methylated in U937, and unmethylated in HL60 and Jurkat. At diagnosis, p21 methylation was not detected in any case of AML or ALL. p27 methylation occurred in 2 (4%) AML patients and in 1 (4%) ALL patient. p57 methylation occurred in 1 (2%) AML patient and in 1 (4%) ALL patient. Therefore, methylation inactivation of the INK4/CDK/RB pathway in leukemia is infrequent. A review of the literature showed a marked variation in the frequencies of methylation of these genes, which might be attributable to difference in methodologies used to detect gene methylation.     

Expression of complement regulatory proteins CR1, DAF, MCP and CD59 in haematological malignancies

Host cells are protected from the lytic effect of the complement system by complement regulatory proteins. This study was designed to investigate the expression of complement regulatory proteins on leukemic blasts which may be susceptible to the lytic effects of the complement system in the circulation. The surface expressions of complement regulatory proteins, complement receptor 1 (CR1, CD35), decay accelerating factor (DAF, CD55), and homologous restriction factor 20 (HRF20, CD59), on peripheral blood and bone marrow blasts were evaluated by using flow cytometry in 16 acute myeloblastic leukemia (AML), 16 acute lymphoblastic leukemia (ALL), 4 chronic lymphocytic leukemia (CLL), 3 chronic myelocytic leukemia (CML) patients and control granulocytes and lymphocytes obtained from 15 healthy volunteers. mRNA expression was investigated by Northern blot analysis. mRNA abundances were calculated after normalization according to 28s rRNA. Surface expressions of CRI and DAF were marginally (p = 0.08 and p = 0.08, respectively) lower in AML, and DAF expression was significantly lower (p=0.0008) in ALL patients in comparison to their normal counterparts. Except from a slight increase that is detected for CD59 in CML patients (p=0.06), there was no significant difference between the surface expressions of CD59 in any of the groups studied. Densitometric analysis of autoradiographs obtained from Northern blots revealed that in AML patients, CR1 mRNA expression were 5.5-fold lower than controls (p=0.06), while DAF mRNA expression was significantly higher (p=0.0046). Furthermore, the mRNA expression of CRI in ALL patients was found significantly lower than in the control group (p = 0.0419). None of the values obtained from the other groups were significantly different from each other. These results suggest that leukemic blasts are protected from the lytic attack of the complement system at all levels, since all of the complement membrane regulatory proteins were expressed in all leukemia types (although at lower amounts in some cases), and it is also possible to use CRI and DAF as differentiation markers in acute leukemias.     

Liposomal daunorubicin,fludarabine, and cytarabine (FLAD) as bridge therapy to stem cell transplant in relapsed and refractory acute leukemia

Therapeutic options for patients with relapsed or refractory acute leukemia are still undefined and often unsatisfactory. We report the outcome of 79 patients with relapsed-refractory acute leukemia treated with fludarabine, cytarabine, and liposomal daunorubicin (FLAD regimen) followed by hematopoietic stem cell transplantation (HSCT), when clinically indicated, between May 2000 and January 2013. Forty-one patients had acute myeloid leukemia (AML), and 38 had acute lymphoblastic leukemia (ALL). Two patients with myeloid blast crises of CML and three with lymphoid blast crises were included in the AML and ALL subgroups, respectively. Median age was 48 years (range 13–77). FLAD was well tolerated with negligible, nonhematological toxicity. Six patients (7.5 %) died before response evaluation. Forty-seven patients achieved hematologic complete response (CR). Complete remission rate was 53 and 65 % among AML and ALL patients, respectively. No CR was recorded among 11 refractory AML patients. Twenty-four patients (30 %) underwent HSCT. Nine patients received stem cells from an HLA identical sibling, and 15 from an alternative donor (3 unrelated matched, 12 haploidentical sibling). Median overall survival in AML and ALL patients receiving FLAD therapy was 9 and 8 months, respectively. A 5-year projected OS for patients receiving the whole program (FLAD + HSCT) was 24 % for AML patients (median survival 43 months), 28 % for ALL patients treated in relapse (median survival 15 months), and 0 % for ALL patients treated for refractory disease. In this paper, we show that FLAD seems to be an effective bridge therapy to HSCT for a part of poor prognosis acute leukemia patients. However, prospective studies are needed to confirm our results.     

p16 gene homozygous deletions in acute lymphoblastic leukemia

The p16 protein is a cyclin inhibitor encoded by a gene located in 9p21, which may have antioncogenic properties, and is inactivated by homozygous p16 gene deletion or, less often, point mutation in several types of solid tumors often associated to cytogenetic evidence of 9p21 deletion. We looked for homozygous deletion and point mutation of the p16 gene in acute lymphoblastic leukemia (ALL), where 9p21 deletion or rearrangement are also nonrandom cytogenetic findings. Other hematologic malignancies including acute myeloid leukemia (AML), myelodysplastic syndromes (MDS), chronic lymphocytic leukemia (CLL), and myeloma were also studied. Homozygous deletion of the p16 gene was seen in 9 of the 63 (14%) ALL analyzed, including 6/39 precursor B-ALL, 3/12 T-ALL, and 0/12 Burkitt's ALL. Three of the 7 ALL with 9p rearrangement (including 3 of the 5 patients where this rearrangement was clearly associated to 9p21 monosomy) had homozygous deletion compared to 5 of the 55 patients with normal 9p (the last patient with homozygous deletion was not successfully karyotyped). Single stranded conformation polymorphism analysis of exons 1 and 2 of the p16 gene was performed in 88 cases of ALL, including the 63 patients analyzed by Southern blot. Twenty-six of the cases had 9p rearrangement, associated to 9p21 monosomy in at least 12 cases. A missense point mutation, at codon 49 (nucleotide 164), was seen in only 1 of the 88 patients. No homozygous deletion and no point mutation of the p16 gene was seen in AML, MDS, CLL, and myeloma. Homozygous deletion of interferon alpha genes (situated close to p16 gene in 9p21) was seen in only 3 of the 9 ALL patients with p16 gene homozygous deletion, and none of the ALL without p16 gene homozygous deletion. Our findings suggest that homozygous deletion of the p16 gene is seen in about 15% of ALL cases, is not restricted to cases with cytogenetically detectable 9p deletion, and could have a pathogenetic role in this malignancy. On the other hand, p16 point mutations are very rare in ALL, and we found no p16 homozygous deletions or mutations in the other hematologic malignancies studied.