Novel one-stop multidisciplinary follow-up clinic significantly improves cancer risk management in BRCA1/2 carriers.

The purpose of this study is to measure the impact of a multidisciplinary one-stop follow-up clinic (MDOSC) on breast and ovarian surveillance, risk reducing surgery and enrolment in clinical trials in BRCA1/2 carriers. All BRCA1/2 carriers in our region were invited and chose which specialists to see in our MDOSC offering best practice using clinical protocols based on national guidelines and published data. Uptake was evaluated over 24 months recording numbers of individuals undergoing breast and ovarian surveillance, risk reducing surgery, newly diagnosed cancers, their method of detection and participation in clinical trials. 172 (60%) of invited BRCA1/2 carriers chose to attend the MDOSC. Breast surveillance was initiated in 88% and screening frequency altered in 14% of women to comply with national guidelines. Risk reducing salpingo-oophorectomy was chosen by 47% of women and an additional 39% were considering it. The rate of failure to remove fallopian tubes fell from 15 to 3% of procedures (P < 0.01) and peritoneal washings and serial sectioning of tubes and ovaries rose from 25% and 14% before, to 67% (P < 0.001) and 63% (P < 0.001) procedures, respectively, after initiation of our MDOSC. 24% of women considered and 18% decided to undergo risk reducing mastectomy during the follow-up period. Participation in clinical trials increased significantly from 51 to 229 enrolments (P < 0.001). Our novel MDOSC designed to devise an individually tailored cancer risk management strategy had a high uptake amongst our BRCA1/2 carriers. Attendance resulted in improved breast and ovarian cancer risk management.

Severe exacerbation of multiple self-healing squamous epithelioma (Ferguson-Smith disease) with radiotherapy, which was successfully treated with acitretin.

We describe the challenging case of a patient presenting with extensive, eruptive mid-facial squamous cell carcinomas (SCCs) and keratoacanthomas (KAs) consequent to radiotherapy. Our patient had a personal and family history of multiple KAs and SCCs. Multiple self-healing squamous epithelioma, otherwise known as Ferguson-Smith disease, was diagnosed. This case presented a therapeutic challenge to preserve tissue and avoid severe facial disfigurement. We found oral acitretin to be the treatment of choice.

The TP53 Arg72Pro and MDM2 309G>T polymorphisms are not associated with breast cancer risk in BRCA1 and BRCA2 mutation carriers.

BACKGROUND: The TP53 pathway, in which TP53 and its negative regulator MDM2 are the central elements, has an important role in carcinogenesis, particularly in BRCA1- and BRCA2-mediated carcinogenesis. A single nucleotide polymorphism (SNP) in the promoter region of MDM2 (309T>G, rs2279744) and a coding SNP of TP53 (Arg72Pro, rs1042522) have been shown to be of functional significance. METHODS: To investigate whether these SNPs modify breast cancer risk for BRCA1 and BRCA2 mutation carriers, we pooled genotype data on the TP53 Arg72Pro SNP in 7011 mutation carriers and on the MDM2 309T>G SNP in 2222 mutation carriers from the Consortium of Investigators of Modifiers of BRCA1/2 (CIMBA). Data were analysed using a Cox proportional hazards model within a retrospective likelihood framework. RESULTS: No association was found between these SNPs and breast cancer risk for BRCA1 (TP53: per-allele hazard ratio (HR)=1.01, 95% confidence interval (CI): 0.93-1.10, P(trend)=0.77; MDM2: HR=0.96, 95%CI: 0.84-1.09, P(trend)=0.54) or for BRCA2 mutation carriers (TP53: HR=0.99, 95%CI: 0.87-1.12, P(trend)=0.83; MDM2: HR=0.98, 95%CI: 0.80-1.21, P(trend)=0.88). We also evaluated the potential combined effects of both SNPs on breast cancer risk, however, none of their combined genotypes showed any evidence of association. CONCLUSION: There was no evidence that TP53 Arg72Pro or MDM2 309T>G, either singly or in combination, influence breast cancer risk in BRCA1 or BRCA2 mutation carriers.

Risk reducing mastectomy: outcomes in 10 European centres.

BACKGROUND: Increasingly women at high risk of breast cancer are opting for risk reducing surgery. The aim of this study was to assess the effectiveness of this approach in women at high risk in both carriers and non-carriers of BRCA1/2. METHODS: Data from 10 European centres that offer a genetic counselling and screening service to women at risk were obtained prospectively from 1995. Breast cancer risks were estimated from life tables and a control group of women at risk who did not undergo surgery. RESULTS: The combined centres have data on 550 women who have undergone risk reducing mastectomy with greater than 3334 women years of follow-up. Operations were carried out on women with lifetime risks of 25-80%, with an average expected incidence rate of 1% per year. No breast cancers have occurred in this cohort in the "at risk" unaffected breast, whereas >34 would have been expected. A high rate (2-3.6%) of occult disease was identified in the at risk breast at the time of surgery. INTERPRETATION: We conclude that risk reducing surgery is highly effective.

Predicting the likelihood of carrying a BRCA1 or BRCA2 mutation: validation of BOADICEA, BRCAPRO, IBIS, Myriad and the Manchester scoring system using data from UK genetics clinics.

OBJECTIVES: Genetic testing for the breast and ovarian cancer susceptibility genes BRCA1 and BRCA2 has important implications for the clinical management of people found to carry a mutation. However, genetic testing is expensive and may be associated with adverse psychosocial effects. To provide a cost-efficient and clinically appropriate genetic counselling service, genetic testing should be targeted at those individuals most likely to carry pathogenic mutations. Several algorithms that predict the likelihood of carrying a BRCA1 or a BRCA2 mutation are currently used in clinical practice to identify such individuals. DESIGN: We evaluated the performance of the carrier prediction algorithms BOADICEA, BRCAPRO, IBIS, the Manchester scoring system and Myriad tables, using 1934 families seen in cancer genetics clinics in the UK in whom an index patient had been screened for BRCA1 and/or BRCA2 mutations. The models were evaluated for calibration, discrimination and accuracy of the predictions. RESULTS: Of the five algorithms, only BOADICEA predicted the overall observed number of mutations detected accurately (ie, was well calibrated). BOADICEA also provided the best discrimination, being significantly better (p<0.05) than all models except BRCAPRO (area under the receiver operating characteristic curve statistics: BOADICEA = 0.77, BRCAPRO = 0.76, IBIS = 0.74, Manchester = 0.75, Myriad = 0.72). All models underpredicted the number of BRCA1 and BRCA2 mutations in the low estimated risk category. CONCLUSIONS: Carrier prediction algorithms provide a rational basis for counselling individuals likely to carry BRCA1 or BRCA2 mutations. Their widespread use would improve equity of access and the cost-effectiveness of genetic testing.

Mosaicism in neurofibromatosis type 2: an update of risk based on uni/bilaterality of vestibular schwannoma at presentation and sensitive mutation analysis including multiple ligation-dependent probe amplification.

BACKGROUND: Neurofibromatosis type 2 (NF2) is almost unique among inherited disorders in the frequency of mosaicism in the first affected generation. However, the implications of this on transmission risks have not been fully elucidated. METHODS: The expanded database of 460 families with NF2 and 704 affected individuals was analysed for mosaicism and transmission risks to offspring. RESULTS: 64 mosaic patients, with a projected mosaicism rate of 33% for sporadic classical NF2 with bilateral vestibular schwannoma at presentation and 60% for those presenting unilaterally, were identified. Offspring risks can be radically reduced on the basis of a sensitive mutation analysis of blood DNA including multiple ligation-dependent probe amplification (MLPA, which detects 15% of all mutations), but even MLPA cannot detect high levels of mosaicism. CONCLUSION: The chances of mosaicism in NF2 and the resultant risks of transmission of the mutation to offspring in a number of different clinical situations have been further delineated. The use of MLPA in this large NF2 series is also reported for the first time.

Evidence-based management options for women at increased breast/ovarian cancer risk.

Recent developments in our ability to predict breast cancer risk necessitates primary care physicians learn to evaluate breast cancer risk and its importance in shaping decisions concerning surveillance and risk reduction measures. This article reviews the current opinion on risk assessment and management of women with an increased risk of breast/ovarian cancer. Management options are given for women at slightly, moderately and highly elevated breast cancer risk, as well as for BRCA1/2 carriers, based on currently available evidence.

Weekly x 4 induction therapy with the anti-CD20 antibody rituximab: effect on circulating t(14;18)(+) follicular lymphoma cells.

Rituximab 375 mg/m(2) weekly x 4 has been reported to induce a 60% response rate in patients with relapsed follicular lymphomas (FL). Our aim was to examine the effect of this rituximab schedule on circulating FL cells in an ongoing multicenter study. One hundred fifty-four patients with FL were examined by nested polymerase chain reaction (PCR) at baseline for the presence of t(14;18) translocation-carrying lymphoma cells in bone marrow and/or blood. Sixty-four patients (42%) had PCR-detectable t(14;18)(+) FL cells. Pretreatment characteristics of these 64 patients were as follows: one had stage I, nine had stage II, 14 had stage III, and 40 had stage IV disease. Thirty-five patients had bulky disease (> or = 5 cm) and 25 patients had an elevated serum lactate dehydrogenase (LDH) level. Bone marrow was morphologically assessed in 64 patients, and 39 of these patients had an infiltration with FL cells. Blood samples from 51 patients were available for PCR analysis between weeks 8-12 after induction therapy, and 28 of these patients (55%) were PCR negative. Paired blood and bone marrow samples were available for PCR analysis from 39 patients between weeks 8-12 after induction therapy with rituximab. Thirteen of these patients (33%) did not have PCR-detectable cells in blood and bone marrow, while 26 patients (67%) still had circulating t(14;18)(+) cells in either bone marrow (eight patients), blood (one patient), or both (17 patients). PCR negativity in blood and bone marrow in 13 patients was statistically significantly associated with partial or complete response after induction therapy with rituximab (P = 0.006). However, clearance of PCR-detectable t(14;18)(+) cells in bone marrow and/or blood could not be associated with any low tumor burden pretreatment characteristics such as stages I/II, absence of morphological bone marrow infiltration or tumor bulk of > or = 5 cm, and normal serum LDH.

Cancer genetics in oncology practice.

Cancer is a genetic disease caused by the progressive accumulation of mutations in critical genes that control cell growth and differentiation. Completion of the Human Genome Project promises to revolutionize the practice of Medicine, especially Oncology care. The tremendous gains in the knowledge of the structure and function of human genes will surely impact the diagnosis, prognosis and treatment of cancer. Moreover, it will lead to more effective cancer control through the use of genetics to quantify individual cancer risks. This article reviews the current status of genetic testing and counseling for cancer risk assessment and will suggest a framework for integrating such counseling into oncology practice.

Organizing cancer genetics programs: the Swiss model.

PURPOSE: Inherited predisposition to cancer is a complex issue, and risk assessment, counseling, and management are multidisciplinary tasks. An infrastructure is needed through which clinical services may be delivered and research activities conducted. METHODS: The Swiss Institute for Applied Cancer Research (SIAK) Network for Cancer Predisposition Testing and Counseling was established in 1999. The goals of the Network are to set common standards for clinical services, to coordinate research activities, to address psychosocial and ethical issues concerning genetic counseling and testing, and to translate the knowledge gained into medical practice. RESULTS: An algorithm for genetic testing and counseling of the families studied by the SIAK Network centers has been established in a consensual process. Eight regional centers currently operate according to this algorithm. Furthermore, a proposal has been submitted for the setup of a Swiss databank for the characterization of BRCA1 and BRCA2 mutation patterns and the identification of potentially unique mutations in probands who seek genetic counseling and testing at the respective centers of the SIAK Network. CONCLUSION: Our coordinated effort will ensure state-of-the-art genetic testing and counseling services in Switzerland and will allow us to acquire knowledge for appropriate risk assessment and surveillance/prevention strategies for individuals with an inherited cancer predisposition.

The effect of Rituximab on patients with follicular and mantle-cell lymphoma. Swiss Group for Clinical Cancer Research (SAKK).

BACKGROUND: Clinical activity of the anti CD-20 monoclonal antibody Rituximab has been reported in patients with follicular lymphoma (FL) and mantle-cell lymphoma (MCL). PATIENTS AND METHODS: 120 patients with bi-dimensionally measurable FL or MCL (R.E.A.L. Classification) were treated with Rituximab 375 mg/m2/week for 4 weeks. A central pathology review confirmed the diagnosis of FL in 76 of 78 and of MCL in 39 of 42 cases. The response was evaluated after 8 weeks and confirmed after 12 weeks from the start of treatment. RESULTS: The toxicity of the treatment was, as expected, grade 1-2 fever and rigors during the first infusion and mild asthenia during the treatment period. Serious adverse events, probably or possibly related to the study treatment, included four deaths (3 of cardiac origin, 1 caused by P. carinii pneumonia) and 10 further nonfatal cases, including a permanent agranulocytosis and one case of heart failure. Response rate at week 12 was 52% for FL and 22% for MCL. After treatment, the BCL-2 rearrangement disappeared in 15 of 29 blood but only in 5 of 23 bone marrow samples; BCL-1 disappeared in 5 of 12 blood and 0 of 7 bone marrow specimens, as determined by PCR. CONCLUSIONS: Rituximab is an active agent for the treatment of FL, while its efficacy is modest in MCL. The effect in reducing minimal residual disease is more pronounced on the blood than it is on the bone marrow.

Involvement of the CD27-CD70 co-stimulatory pathway in allogeneic T-cell response to follicular lymphoma cells.

Non-activated follicular lymphoma (FL) cells do not function as effective antigen-presenting cells in vivo. CD40 activation of FL cells up-regulates critical adhesion and co-stimulatory molecules, thereby inducing lymphoma-specific cytotoxic T cells in vitro. However, other evidence suggests that CD70 is another important co-stimulatory molecule involved in antigen dependent T-cell activation. Here, we showed that freshly isolated FL cells from eight diagnostic biopsies expressed intermediate to high levels of CD27, whereas only insignificant levels of CD70 were detected on their cell surface. Together with the low to intermediate expression of B7, these findings help to explain the poor antigen-presenting capacity of non-activated FL cells. Activation of FL cells by CD27 and CD40 induced a significantly higher alloantigen T-cell response than CD40 alone, whereas CD27 activation induced only a mostly insignificant T-cell proliferation. Both CD40 and CD27 + CD40 activation resulted in a high up-regulation of CD70 and B7 molecules, whereas CD27 activation up-regulated CD70 but not B7 expression on the surface of FL cells. Thus, expression of both CD70 and B7 co-stimulatory molecules appears to be essential for an efficient T-cell-mediated immune response. However, the molecules responsible for the significantly higher alloantigen T-cell response to FL cells activated through CD27 and CD40 remain to be identified. In summary, we conclude that CD27+CD70 represents another co-stimulatory pathway involved in T-cell-mediated immune responses to FL cells. Our findings suggest that several co-stimulatory pathways exist and should be taken into consideration to optimize antigen presentation for the generation of lymphoma-directed cytotoxic T cells for adoptive immunotherapy.

A prospective study of risk-adapted therapy for large cell non-Hodgkin's lymphoma with VACOP-B followed by high-dose CBV and autologous progenitor cell transplantation for high-risk patients in remission.

Several centres reported a favourable outcome after high-dose chemotherapy with autologous progenitor cell transplantation in selected patients with high-risk large cell non-Hodgkin's lymphoma in first remission. Based on these observations, we wanted to prospectively determine the outcome of a risk-adapted therapy for patients with large cell lymphoma. Patients aged 60 years or less received 12 weeks of VACOP-B chemotherapy. For high-risk patients in remission this was immediately followed by high-dose chemotherapy with cyclophosphamide, carmustine and etoposide and autologous progenitor cell transplantation. High-risk criteria were defined before the establishment of the International Index and included large cell lymphoma stage III or IV or mediastinal large lymphoma with sclerosis stage II or higher, and the presence of bulky tumours and/or an elevated LDH. 89 patients fulfilled the clinical selection criteria and were entered onto this multicentre study. 82 patients were evaluable after confirmation of large cell histology by pathology review. Of these, 51 were considered to be in the low-risk group and 31 in the high-risk group. The 3-year event-free survival for all patients was 68%. The 3-year event-free survival was 76% for the low-risk and 55% for the high-risk group (P = 0.061). Only 22/31 high-risk patients were able to receive the high-dose chemotherapy in first remission as intended. In conclusion, although our study demonstrated that a risk-adapted therapy for large cell lymphoma could be safely administered, the potential impact on outcome of the strategy chosen here is likely to be small.

Selection and immunomagnetic purging of peripheral blood CD34+ cells for autologous transplantation in B-cell non-Hodgkin's lymphomas.

BACKGROUND: Clonogenic tumor cells in the hematopoietic progenitor cell harvest may contribute to relapse after high dose therapy for B-cell malignancies. Purging of the HPC harvest requires large amounts of anti-B-cell antibodies, whereas CD34-selection enriches self renewing HPC's but malignant cells are still detectable in many CD34+ fractions. PATIENTS AND METHODS: We examined the feasibility and safety of a CD34-selection followed by purging with anti B-cell antibodies in 11 patients with B-cell non-Hodgkin's lymphomas undergoing high-dose therapy with cyclophosphamide, BCNU and etoposide with retransfusion of autologous HPC's. RESULTS: A mean number of 340 x 10(8) mononuclear cells was used for CD34-selection and immunomagnetic purging. CD34+ cells were enriched from a mean of 1.7% (range 0.2%-4.5%) to a mean of 68% (range 49%-87%) with a mean recovery of 27% (range 15%-43%). The mean number of retransfused CD34+ cells was 1.2 x 10(6)/kg (range 0.6-2.2 x 10(6)/kg) body weight with a median of 11 days (range 10-13 days) to neutrophil recovery of 0.5 x 10(9)/l and 17 days (range 13-25 days) to platelet recovery of 50 x 10(9)/l. Mean number of intravenous antibodies and inpatient days were 8 (range 0-14) and 22 (range 19-26) respectively. Major toxicity consisted in four septicemias. CONCLUSIONS: CD34-selected and purged HPC's are safe and mediate rapid hematological recovery after high dose therapy for B-cell non-Hodgkin's lymphomas.

T-cell derived cytokines co-stimulate proliferation of CD40-activated germinal centre as well as follicular lymphoma cells.

Follicular lymphomas, the malignant counterparts of normal germinal centre (GC) B-cells, grow in vivo in close association with polyclonal T-cells, predominantly from the T-helper cell type. T-cell-derived growth factors are involved in the development of GC B-cells. However, their role in the pathogenesis of follicular lymphomas has not been clearly defined. We investigated the co-stimulatory activity of 14 cytokines (interleukin-1 to -8, IL-10, IL-13, INF-alpha, TNF-alpha, GM-CSF and SCF) on the proliferation of CD40-activated follicular lymphoma cells in comparison to tonsillar GC B-cells. Tonsillar GC B-cells (n = 4), malignant cells from diagnostic lymph node biopsies of patients with follicular (n = 4) or transformed (n = 4) lymphomas were grown on irradiated CD40-ligand transfectants, with and without cytokines. [3H]-thymidine uptake was measured at day 7. IL-10 and IL-4 proved to be the most potent co-stimulators of proliferation of tonsillar GC B-cells, whereas proliferation of follicular lymphoma cells was co-stimulated by IL-4. The fact that IL-4 is a T-cell derived cytokine, suggests that lymphoma infiltrating T-cells play a role in the growth of these malignancies. Moreover, proliferation of both non-neoplastic tonsillar GC B-cells and follicular lymphomas is co-stimulated by T-cell derived cytokines, indicating that responsiveness to paracrine factors may not be a characteristic of the malignant phenotype.

Fate of contaminating t(14; 18)+ lymphoma cells during ex vivo expansion of CD34-selected hematopoietic progenitor cells.

The use of ex vivo expanded CD34-selected hematopoietic progenitor cells (HPCs) for autologous stem cell support or gene therapy is a major area of research and is likely to increase in the future. At present, little is known about the fate of contaminating malignant cells during ex vivo expansion of CD34-selected HPCs. We established a competitive polymerase chain reaction (PCR) titration assay to determine the number of residual lymphoma cells before and after selection and ex vivo expansion of CD34-selected HPCs in patients with t(14; 18) translocation carrying non-Hodgkin's lymphoma. Seven bone marrow (BM) and 2 mobilized peripheral blood progenitor cell samples from 8 patients without histologic BM involvement at the time of the harvest were analyzed by competitive PCR titration assay and determined to contain between < or = 10 and 4,000 lymphoma cells/ 10(6) mononuclear cells (MNCs). Immunoadsorption enriched CD34+ cells from a mean of 5% (range, 1% to 9%) to a mean of 88% (range, 76% to 94%) of MNCs and resulted in a 1 to 4 log depletion of contaminating tumor cells. Two HPC samples became PCR negative after CD34 selection, whereas 7 samples still contained < or = 10 to 200 residual lymphoma cells/10(5) MNCs. CD34-selected cells were consecutively expanded in suspension culture in the presence of stem cell factor, interleukin-1 beta (IL-1 beta), IL-3, and IL-6. The mean increase of cells was 13-fold (range, 4- to 22-fold) at day 7 and 65-fold (range, 43- to 110-fold) at day 14 of culture. Expansion resulted predominantly in myelomonocytic differentiation, whereas B-cell antigen-expressing cells became undetectable. Six of the seven PCR-positive CD34-selected samples became PCR-negative for the t(14; 18) translocation at day 7 and/or 14 of expansion. One PCR-positive and one PCR-negative CD34-selected sample were PCR-positive after ex vivo expansion, but the number of residual lymphoma cells remained at the limit of detection. We conclude that CD34-selection does not eliminate contaminating lymphoma cells in the majority of t(14; 18)+ HPC harvests. However, during ex vivo expansion of CD34-selected HPCs, residual t(14; 18)+ lymphoma cells do not proliferate and become undetectable by PCR in the majority of cases.

Distinct patterns of minimal residual disease associated with graft-versus-host disease after allogeneic bone marrow transplantation for chronic myelogenous leukemia.

PURPOSE: Allogeneic bone marrow transplantation (BMT) has been shown to provide effective therapy for chronic myelogenous leukemia (CML), but previous reports have also demonstrated the persistence of bcr-abl-positive cells for months to years after BMT in the majority of patients. To evaluate the biologic significance of persistent bcr-abl-positive cells, we examined the relationship between clinical parameters known to affect the risk of relapse and the ability to detect bcr-abl-positive cells post-BMT. PATIENTS AND METHODS: We analyzed 480 samples from 92 patients at two transplant centers for the presence of bcr-abl-positive cells by polymerase chain reaction (PCR). Two different BMT preparative regimens and protocols for prevention of graft-versus-host disease (GVHD) were used. One center used cyclophosphamide plus total-body irradiation (CY/TBI) and T-cell-depleted marrow; the second center used busulfan plus cyclophosphamide (Bu/CY) and untreated marrow with cyclosporine and methotrexate (Csp/MTX) as GVHD prophylaxis. RESULTS: We first determined the percent of patients at each center with > or = one PCR-positive (PCR+) result at defined intervals post-BMT. Between 0 and 6 months post-BMT, the majority of patients (80% to 83%) in both populations had PCR-detectable bcr-abl-positive cells. Between 6 and 24 months post-BMT, 80% to 88% of patients who received T-cell-depleted marrow remained PCR+, as compared with 26% to 30% of patients who received unmodified marrow. After 24 months post-BMT, the percentage of PCR+ patients was not significantly different in the two populations. This pattern of detection of bcr-abl-positive cells post-BMT followed the development of chronic GVHD in patients who received unmodified marrow. All patients were also divided into three groups based on post-BMT PCR results as follows: (1) persistent PCR+ (n = 29), (2) intermittent PCR-negative ([PCR-] n = 40), and (3) persistent PCR- (n = 23). These three groups were found to have a low, intermediate, and high probability of maintaining remission and disease-free survival, respectively (P = .0001). Intermittent or persistent PCR- results, which reflect levels of minimal residual disease < or = the limit of detection by PCR, were clearly associated with both acute (P = .004) and chronic (P = .000005) GVHD. Nevertheless, 44% of patients without GVHD also had intermittent or persistent PCR- assays. CONCLUSION: The persistence of PCR-detectable bcr-abl-positive cells early post-BMT in more than 80% of patients suggests that neither BMT preparative regimen effectively eradicates CML cells in most patients. Subsequently, acute and/or chronic GVHD are associated with a decreased ability to detect residual bcr-abl-positive cells, which suggests that immunologic mechanisms mediated by donor cells are important for inducing long-term remissions after BMT. The demonstration that 44% of patients without GVHD had either low or undetectable levels of residual leukemia suggests the presence of mechanisms capable of suppression or eradication of CML independent of GVHD.

Functional consequences of APO-1/Fas (CD95) antigen expression by normal and neoplastic hematopoietic cells.

Murine monoclonal antibody (mAb) 7C11 binds to the same cell surface epitope as anti-APO-1 and anti-Fas and reacts specifically with cells transfected with a cDNA encoding the human Fas antigen. Furthermore, incubation with 7C11 causes death of hematopoietic cell lines that express APO-1/Fas but not APO-1/Fas-negative cell lines. 7C11 therefore recognizes the human APO-1/Fas (CD95) antigen, a 40 to 50 kDa cell surface glycoprotein that can trigger apoptosis or programmed cell death. Expression of APO-1/Fas antigen by normal and neoplastic hematopoietic cells was determined by flow cytometry using 7C11. APO-1/Fas is expressed by approximately 30 to 40% of resting peripheral blood T cells, B cells, and monocytes and by approximately 5% of resting NK cells and thymocytes. It was not detected on granulocytes, erythrocytes, or platelets. Approximately 80 to 90% of activated T cells, B cells, and thymocytes express APO-1/Fas, as do the majority of activated NK cells. Perturbation of APO-1/Fas by 7C11 does not affect the viability of resting lymphocytes or monocytes. In contrast, activated T cells and NK cells undergo apoptosis within 3 hours of exposure to 7C11. Other mAb that stimulate T cells or NK cells do not cause rapid induction of programmed cell death. APO-1/Fas antigen is expressed by many cell lines of lymphoid and myeloid lineage. However, this antigen was detected on neoplastic cells from only one of 69 patients with acute myeloid leukemia, acute lymphoblastic leukemia, chronic myelogenous leukemia, chronic lymphocytic leukemia, or multiple myeloma. Only 3 out of 25 tumor samples from patients with non-Hodgkin's lymphoma were found to express APO-1/Fas. All three of these lymphomas harbored the bcl-2-Ig fusion gene associated with the chromosomal translocation t (14;18). Conversely, only 27% of lymphomas that possessed the bcl-2-Ig gene were found to express the APO-1/Fas antigen. Like normal activated lymphocytes, leukemia and lymphoma cells that expressed APO-1/Fas antigen were found to undergo apoptosis in vitro after incubation with 7C11. The APO-1/Fas antigen appears to regulate the growth of normal hematopoietic cells, and the marked upregulation of this antigen on activated normal lymphocytes contrasts sharply with the absence of APO-1/Fas on neoplastic cells of hematopoietic lineage. Defects in the apoptotic signal delivered through this antigen might contribute to the pathogenesis of hematopoietic neoplasms. Thus, the gene encoding APO-1/Fas can be considered a novel type of tumor suppressor gene, just as bcl-2 can be considered a cellular proto-oncogene.