Effectiveness of antibacterial prophylaxis during induction chemotherapy in children with acute lymphoblastic leukemia

BACKGROUND

Pediatric patients receiving induction chemotherapy for newly diagnosed acute lymphoblastic leukemia (ALL) are at high risk of developing life-threatening infections. We investigated whether uniform antibacterial guidelines, including mandatory antibacterial prophylaxis in afebrile patients during induction, decreases the incidence of microbiologically documented bacteremia.

METHODS

Between 2012 and 2015, 230 patients with newly diagnosed ALL (aged 1-21) were enrolled on Dana-Farber Cancer Institute ALL Consortium Protocol 11-001 (DFCI 11-001). Induction therapy, regardless of risk group, included vincristine, prednisone, doxorubicin, methotrexate, and PEG-asparaginase. Afebrile patients received fluoroquinolone prophylaxis at the initiation of induction and those presenting with fever received broad-spectrum antibiotics; antibiotics were continued until blood count recovery. Rates of documented bacteremias and fungal infections on DFCI 11-001 were compared to those on the predecessor protocol (DFCI 05-001), which included the same induction phase without antibiotic prophylaxis guidelines.

RESULTS

Sixty-six (28.7%) patients received fluoroquinolone prophylaxis, the remaining patients received broad-spectrum antibiotics. Twenty-four (36.4%) patients on prophylaxis developed fever and seven (10.6%) developed bacteremia. The overall rate of infection during induction on DFCI 11-001 was lower than on DFCl 05-001 (14.3% vs. 26.3%, P < 0.0001) due to a decreased rate of bacteremia (10.9% vs. 24.4%, P < 0.0001). The rate of fungal infections (4.8% vs. 3.6%) and induction death (0.9% vs. 2%) was not significantly different.

CONCLUSION

For children with newly diagnosed ALL, uniform antibiotic administration until blood count recovery, including fluoroquinolone prophylaxis for afebrile patients, reduced the incidence of bacteremia during the induction phase. Larger, randomized studies should be performed to confirm these findings.

Impact of baseline clinical and laboratory features on the risk of thrombosis in children with acute lymphoblastic leukemia: A prospective evaluation

BACKGROUND

Children with acute lymphoblastic leukemia (ALL) have increased risk of thromboembolism (TE). However, the predictors of ALL-associated TE are as yet uncertain.

OBJECTIVE

This exploratory, prospective cohort study evaluated the effects of clinical (age, gender, ALL risk group) and laboratory variables (hematological parameters, ABO blood group, inherited and acquired prothrombotic defects [PDs]) at diagnosis on the development of symptomatic TE (sTE) in children (aged 1 to ≤18) treated on the Dana-Farber Cancer Institute ALL 05-001 study.

PROCEDURES

Samples collected prior to the start of ALL therapy were evaluated for genetic and acquired PDs (proteins C and S, antithrombin, procoagulant factors VIII (FVIII:C), IX, XI and von Willebrand factor antigen levels, gene polymorphisms of factor V G1691A, prothrombin gene G20210A and methylene tetrahydrofolate reductase C677T, anticardiolipin antibodies, fasting lipoprotein(a), and homocysteine).

RESULTS

Of 131 enrolled patients (mean age [range] 6.4 [1-17] years) 70 were male patients and 20 patients (15%) developed sTE. Acquired or inherited PD had no impact on the risk of sTE. Multivariable analyses identified older age (odds ratio [OR] 1.13; 95% confidence interval [CI]: 1.01, 1.26) and non-O blood group (OR 3.64, 95% CI: 1.06, 12.51) as independent predictors for development of sTE. Patients with circulating blasts had higher odds of developing sTE (OR 6.66; 95% CI: 0.82, 53.85).

CONCLUSION

Older age, non-O blood group, and presence of circulating blasts, but not PDs, predicted the risk of sTE during ALL therapy. We recommend evaluation of these novel risk factors in the development of ALL-associated TE. If confirmed, these easily accessible variables at diagnosis can help develop a risk-prediction model for ALL-associated TE.

The IVAIRE project--a randomized controlled study of the impact of ventilation on indoor air quality and the respiratory symptoms of asthmatic children in single family homes

A randomized controlled trial was carried out to measure the impact of an intervention on ventilation, indoor air contaminants, and asthma symptoms of children. Eighty-three asthmatic children living in low-ventilated homes were followed over 2 years. Several environmental parameters were measured during the summer, fall, and winter. The children were randomized after Year 1 (43 Intervention; 40 Control). The intervention included the installation of either a Heat Recovery Ventilator (HRV) or Energy Recovery Ventilator (ERV). During the fall and winter seasons, there was a significant increase in the mean ventilation rate in the homes of the intervention group. A statistically significant reduction in mean formaldehyde, airborne mold spores, toluene, styrene, limonene, and α-pinene concentrations was observed in the intervention group. There was no significant group difference in change in the number of days with symptoms per 14 days. However, there was a significant decrease in the proportion of children who experienced any wheezing (≥1 episode) and those with ≥4 episodes in the 12-month period in the intervention group. This study indicates that improved ventilation reduces air contaminants and may prevent wheezing. Due to lack of power, a bigger study is needed.

PRACTICAL IMPLICATIONS

Positive findings from this study include the fact that, upon recruitment, most of the single family homes with asthmatic children were already equipped with a mechanical ventilation system and had relatively good indoor air quality. However, the 8-h indoor guideline for formaldehyde (50 μg/m3) was frequently exceeded and the ventilation rates were low in most of the homes, even those with a ventilation system. Both ERVs and HRVs were equally effective at increasing air exchange rates above 0.30 ACH and at preventing formaldehyde concentrations from exceeding the 50 μg/m3 guideline during the fall and winter seasons. Furthermore, the ERVs were effective at preventing excessively low relative humidities in the homes. Based on observed difference of risk, intervention to increase ventilation in five sample homes and children would prevent 1 home to exceed the indoor air long-term formaldehyde guideline and prevent 1 asthmatic child experiencing at least one episode of wheezing over a year.

Biological aspects of neuroblastomas identified by mass screening in Quebec

BACKGROUND

Neuroblastoma has several characteristics that suggest that preclinical diagnosis might improve outcome. Therefore, the Quebec Neuroblastoma Screening Project was undertaken from 1989 to 1994 to examine infants at 3 weeks and 6 months by measuring urinary catecholamine metabolites.

PROCEDURE

Over the 5-yr period, 45 tumors were detected by screening, 20 were identified clinically prior to the third week, and 64 were identified clinically at a later time. We analyzed available tumors for Shimada histopathology, tumor ploidy, MYCN copy number and serum ferritin.

RESULTS

Of the tumors detected by screening, only 2 of 45 tested had unfavorable histology, 2 of 45 had diploid or tetraploid DNA content, 0 of 43 had MYCN amplification, and 4 of 44 had elevated serum ferritin. All of these patients are alive and well. The 20 patients detected prior to the 3-week screen had similar biological characteristics. In contrast, of the patients detected clinically after 3 weeks of age, 19 of 51 testedhad unfavorable histology, 25 of 66 had diploid or tetraploid tumors, 12 of 56 had MYCN amplification, and 14 of 54 had elevated ferritin.

CONCLUSIONS

The difference between the screened and clinically detected cases was highly significant for each biological variable. Preliminary data on other biological variables, such as neurotrophin expression and allelic loss on 1 p in these patients are consistent with the above findings. These data suggest that mass screening for neuroblastoma at or before 6 months of age detects almost exclusively tumors that have favorable biological characteristics, many of which might have regressed spontaneously. Thus, continued mass screening for neuroblastoma at 6 months is unlikely to accomplish its intended goal, and should probably be discontinued.

Toxicity profile of interferon alfa-2b in children: A prospective evaluation

The toxicity of interferon (IFN) alfa-2b therapy was prospectively evaluated in 53 children treated from 1991 to 1996 in 2 successive studies of IFN alfa therapy for severe hemangiomas at Sainte-Justine Hospital. Toxicity was generally mild and transient, with grade 1 toxicity occurring in 100% of patients, grade 2 toxicity in 89%, grade 3 toxicity in 58%, and grade 4 toxicity in 17%. Ten of 43 patients available for evaluation had an abnormal neurologic examination. Severe neurotoxicity in the form of spastic diplegia occurred in one patient. In conclusion, IFN alfa therapy is generally well tolerated in children. However, it may rarely be associated with severe toxicity and must be used with caution.

Amplifications of DNA primase 1 (PRIM1) in human osteosarcoma

We studied the involvement of PRIM1 in osteosarcoma by differential display, Northern and Southern hybridization, as well as fluorescence in situ hybridization (FISH) on interphase nuclei. In total, 22 pediatric oncology specimens were tested. PRIM1 was found to be amplified in 41% of the samples. PRIM1 is coamplified with the core 12q13 amplicon genes CDK4, SAS, and OS9, and was physically mapped very close to them. PRIM1 is therefore a new candidate for the role of a major target gene of 12q13 amplifications in human cancers. Genes Chromosomes Cancer 26:62-69, 1999.

Open-label comparison of the antiemetic efficacy of single intravenous doses of dolasetron mesylate in pediatric cancer patients receiving moderately to highly emetogenic chemotherapy

BACKGROUND

Nausea and vomiting are among the most unpleasant adverse side effects of cancer therapy.

PROCEDURE

An open-label dose-escalation study was conducted to assess the appropriate intravenous dose of dolasetron for pediatric patients undergoing chemotherapy. Patients received dolasetron in single intravenous doses of 0.6 (n = 10), 1.2 (n = 12), 1.8 (n = 12), or 2.4 (n = 12) mg/kg 30 min before receiving emetogenic chemotherapy. Pharmacokinetic parameters were evaluated at each dose level and efficacy was evaluated over the first 24 hr following the administration of dolasetron.

RESULTS

A complete response was achieved in 10% of patients given 0.6 mg/kg, 25% of patients given 1. 2 mg/kg, 67% of patients given 1.8 mg/kg, and 33% of patients given 2.4 mg/kg. Peak plasma concentrations (Cmax) were observed between 0. 33 and 0.75 hr following dolasetron infusion. Cmax and area under plasma concentration-time (AUC) increased with larger doses of dolasetron, while terminal disposition half-life (t1/2) and apparent clearance (Clapp) were not significantly changed with respect to dose. For 1.8-mg/kg dolasetron, the t1/2 was 4.98 hr and the maximum plasma concentration (tmax) 0.47 hr. Adverse events were mild to moderate. No serious events occurred. Conclusions. This study suggests that a single intravenous dose of 1.8 mg/kg is the optimum single intravenous dose for controlling chemotherapy-induced emesis in pediatric patients.

Safety, tolerability, antiemetic efficacy, and pharmacokinetics of oral dolasetron mesylate in pediatric cancer patients receiving moderately to highly emetogenic chemotherapy

PURPOSE

The safety, antiemetic efficacy, and pharmacokinetics of single oral doses of dolasetron, a new highly selective 5-HT3 receptor antagonist, were evaluated in children with cancer undergoing treatment with moderately to highly emetogenic chemotherapy.

PATIENTS AND METHODS

A total of 32 children, ages 3 to 18 years, were enrolled in a nonrandomized, multicenter, open-label, dose-escalation study. Three oral dose levels (0.6, 1.2, or 1.8 mg/kg) were studied. Safety, efficacy, and pharmacokinetic parameters were assessed over 24 hours at each dosage level.

RESULTS

The most effective dose was 1.8 mg/kg; 60% of the patients achieved a complete or major response (< or =2 emetic episodes in 24 hours). A complete response was achieved in 3 of 9 patients (33%) who received 0.6 mg/kg, 4 of 13 (31%) patients who received 1.2 mg/kg, and 5 of 10 (50%) patients who received 1.8 mg/kg of dolasetron. Overall, dolasetron was well tolerated. Adverse events were mild and similar to those reported in adults. Peak plasma concentrations (Cmax) of dolasetron's active reduced metabolite, MDL 74,156, were dose proportional and occurred, on the average, within 1 hour of oral administration. The half-life (t1/2) in plasma was approximately 6 hours for all dose levels, and the mean clearance (CLapp) was unrelated to dose.

CONCLUSIONS

Oral dolasetron is safe and effective in reducing chemotherapy-induced nausea and vomiting, particularly at the 1.8-mg/kg dose level. These results support further evaluation of oral dolasetron in larger randomized clinical trials in the pediatric cancer population.

Pathology review of screening negative neuroblastomas: a report from the Quebec Neuroblastoma Screening Project

BACKGROUND

The Quebec Neuroblastoma Screening (QNS) Project completed a 5-year program for measuring urinary vanillylmandelic acid (VMA)/homovanillic acid (HVA) levels at age 3 weeks and/or 6 months in 89% of 476,603 Quebec-born infants from 1989-1994; 45 screening positive preclinical cases (S-positive cases) and 20 congenital/neonatal (C/N) cases were identified. As of April 1997, an additional 59 cases in the same birth cohort were diagnosed clinically; these neuroblastomas developed after screening verified normal VMA/HVA levels (S-negative cases).

METHODS

Pathology specimens from 45 of 59 S-negative cases were reviewed centrally and classified according to the Shimada system. Results were compared with clinical data and also with S-positive and C/N cases.

RESULTS

Of 45 S-negative cases, 27 tumors had favorable histology (FH) and 18 had unfavorable histology (UH). Approximately 52% of FH tumors were diagnosed before age 1 year, whereas UH tumors were nearly exclusively (94%) diagnosed after age 1 year (P < 0.01). Approximately 89% of FH tumors were Stage I, II, or IV-S, whereas 72% UH tumors were Stage III or IV (P < 0.001). All children with FH tumors were alive at last follow-up (range of follow-up period: 9-79 months; median, 35 months), whereas 8 children with UH tumors died of disease even after limited follow-up (range of follow-up period: 0-60 months; median, 20 months). By contrast, S-positive and C/N cases were predominantly (97%) FH tumors, often (76%) Stage I, II, or IV-S, with excellent clinical outcome (survival rate of 98%).

CONCLUSIONS

The majority of the UH neuroblastomas that developed in the birth cohort of the QNS Project were included in the group of S-negative cases and could not be detected by the screening at age 3 weeks and/or 6 months.

Psychometric properties of the Health Utilities Index Mark 2 system in paediatric oncology patients

This study examined the reliability and validity of the Health Utilities Index (HUI) Mark 2 system, a health-related quality of life (QoL) instrument, in children with cancer. The sample consisted of 61 mothers of paediatric oncology patients, aged 4.1-17.3 years, who were either on treatment (n = 20) or off treatment (n = 41). The test-retest reliability was very good for the HUI Mark 2 system global score and all of its dimensions except pain. The HUI Mark 2 dimensions of emotion, pain and self-care as well as its overall score showed moderate convergent validity with other measures. In addition, the HUI Mark 2 system demonstrated good discriminant validity. However, the content validity of the HUI Mark 2 system when considered as a multiattribute descriptive health profile is questionable because it falls to assess domains such as neuropsychological and psychosocial functioning. Overall, the results indicate that the HUI Mark 2 system is reliable and valid as a measure of health-related QoL for paediatric oncology patients.

Survival rates among Canadian children and teenagers with cancer diagnosed between 1985 and 1988

PURPOSE

To describe the survival rates among Canadian children and teenagers with cancer diagnosed between 1985 and 1988 using population-based data, specifically for the more common forms of childhood cancer, and to assess the effect of age at diagnosis and sex as prognostic factors for selected childhood cancers.

DESIGN

Retrospective survival study based on incident cases of cancer identified by the National Cancer Incidence Reporting System and follow-up ascertained by computer record linkage to the Canadian Mortality Database.

SUBJECTS

A total of 4409 patients with cancer first diagnosed at 19 years of age or younger between 1985 and 1988, and followed up to Dec. 31, 1991.

MAIN OUTCOME MEASURES

Survival rates calculated at 1, 3 and 5 years according to the actuarial life table and the proportional hazards models.

RESULTS

The 5-year survival rate for all cancers combined was 71%. Females with acute lymphoblastic leukemia and astrocytoma had markedly higher survival rates than their male counterparts (p < 0.05). Age at diagnosis was a significant predictor of survival among children with acute lymphoblastic leukemia or acute nonlymphoblastic leukemia (p < 0.01), infants having a substantially poorer prognosis than older children. Conversely, the survival rate among infants with neuroblastoma was higher than that among older children, 87% surviving for 5 years after diagnosis.

CONCLUSIONS

The survival rate among Canadian children and teenagers with cancer is favourable in relation to the rate among adults with cancer. Nonetheless, the 5-year survival rates for several childhood cancers remain poor (i.e., less than 65%). The survival rates among Canadian children with cancer are similar to those among children with cancer in other developed countries.

Repeated-dose pharmacokinetics of an oral solution of itraconazole in infants and children

The safety, tolerability, and pharmacokinetics of an oral solution of itraconazole and its active metabolite hydroxyitraconazole were investigated in an open multicenter study of 26 infants and children aged 6 months to 12 years with documented mucosal fungal infections or at risk for the development of invasive fungal disease. The most frequent underlying illness was acute lymphoblastic leukemia, except in the patients aged 6 months to 2 years, of whom six were liver transplant recipients. The patients were treated with itraconazole at a dosage of 5 mg/kg of body weight once daily for 2 weeks. Blood samples were taken after the first dose, during treatment, and up to 8 days after the last itraconazole dose. On day 1, the mean peak concentrations in plasma after the first and last doses (Cmax) and areas under the concentration-time curve from 0 to 24 h (AUC0-24) for itraconazole and hydroxyitraconazole were lower in the children aged 6 months to 2 years than in children aged 2 to 12 years but were comparable on day 14. The mean AUC0-24-based accumulation factors of itraconazole and hydroxyitraconazole from day 1 to 14 ranged from 3.3 to 8.6 and 2.3 to 11.4, respectively. After 14 days of treatment, Cmax, AUC0-24, and the half-life, respectively, were (mean +/- standard deviation) 571+/-416 ng/ml, 6,930+/-5,830 ng.h/ml, and 47+/-55 h in the children aged 6 months to 2 years; 534+/-431 ng/ml, 7,330+/-5,420 ng.h/ml, and 30.6+/-25.3 h in the children aged 2 to 5 years; and 631+/-358 ng/ml, 8,770+/-5,050 ng.h/ml, and 28.3+/-9.6 h in the children aged 5 to 12 years. There was a tendency to have more frequent low minimum concentrations of the drugs in plasma for both itraconazole and hydroxyitraconazole for the children aged 6 months to 2 years. The oral bioavailability of the solubilizer hydroxypropyl-beta-cyclodextrin was less than 1% in the majority of the patients. In conclusion, an itraconazole oral solution given at 5 mg/kg/day provides potentially therapeutic concentrations in plasma, which are, however, substantially lower than those attained in adult cancer patients, and is well tolerated and safe in infants and children.

Recombinant interferon alfa-2b in the treatment of vision-threatening capillary hemangiomas in childhood

INTRODUCTION

Hemangiomas of the orbit and eyelids may cause serious ocular problems usually related to amblyopia and astigmatism. Steroids have become the accepted treatment. However, some hemangiomas are resistant to steroids or require prolonged use,with unacceptable side effects. Interferon alfa-2b, an antiangiogenic protein, was used in this prospective study to treat visually threatening hemangiomas that were unresponsive to oral or intralesional steroid treatment.

METHODS

Forty patients aged 2 to 36 months with life- or organ-threatening hemangiomas were prospectively enrolled to evaluate the efficacy and safety of interferon alfa treatment for hemangiomas. Sixteen of these 40 patients had hemangiomas causing serious ocular dysfunction. The patients were treated with 3 x 10(6) U/m2 interferon alfa-2b subcutaneously daily for 3 months; treatment was then tapered or retreated according to response and protocol. Therapeutic responses were documented.

RESULTS

Fifteen patients with ocular hemangiomas have finished treatment. The pretreatment volume measured by computed axial tomographywas an average of 22.3 cm3. Clinical response with eye opening was observed at an average of 6 weeks. There was a significant regression of the hemangioma in all patients, with an average 82% reduction in volume. Patients were treated with glasses and occlusion therapy as appropriate. Final visual acuities with a follow-up averaging 14 months after cessation of interferon treatment were normal, except that five of 15 patients had amblyopia; one of these patients had 20/40, two had 20/60, and two had 20/70. There were no major illnesses or serious adverse side effects.

CONCLUSION

Interferon alfa-2b treatment resulted in good to excellent regression of all the hemangiomas. This regression was clinically significant,with patients able to open the affected eye an average of 6 weeks into treatment. Visual results were good, with moderate amblyopia occurring only in patients treated at a later age. Interferon alfa-2b was well tolerated by these young patients, and no significant illness or side effect has occurred.

Excess of congenital abnormalities in French-Canadian children with neuroblastoma: a case series study from Montréal

Neuroblastoma is one of the most common cancers of childhood. Some studies have shown an excess of congenital abnormalities in children who have been diagnosed with neuroblastoma. In this study we examined the medical records of all children with neuroblastoma seen at St. Justine Children's Hospital between the years 1977 and 1993. A total of 141 children (131 of French-Canadian ancestry) were included in this study. Twelve children (8.5%) had 21 defined congenital abnormalities (1,490 per 10,000 children). This compared with a rate of 444.3 children with abnormalities per 10,000 live births (4.44%) for all congenital abnormalities in the British Columbia Health Surveillance Registry, 1979-1988 (relative risk = 1.91, P = 0.03). Six of the 12 children had cardiovascular malformations. These and previous results suggest that there may be a common developmental origin to neuroblastoma and to some congenital malformations. Genes that control development may be worthy of further study in these children.

Screening for neuroblastoma is ineffective in reducing the incidence of unfavourable advanced stage disease in older children

Neuroblastoma exhibits many characteristics which would suggest that preclinical detection may improve outcome. The Quebec Neuroblastoma Screening Project was initiated to determine whether mass screening could reduce mortality in a large cohort of infants. All 476,603 children born in the province of Quebec during a 5-year period of time (1 May 1989 to 30 April 1994) were eligible for determinations of urinary catecholamine metabolites at 3 weeks and 6 months of age. Children with positive screening were referred to one of four paediatric cancer centres in Quebec for uniform evaluation and treatment. Standardised incidence ratios (SIRs) were calculated for neuroblastoma in Quebec and two comparable population-based controls during the same period of time using similar ascertainment procedures. Compliance with screening in Quebec was 91% at 3 weeks (n = 425,816) and 74% at 6 months (n = 349,706). Up to 31 July 1995 with a follow-up of the birth cohort of 15-75 months, 118 cases of neuroblastoma were diagnosed, 43 detected preclinically by screening, 20 detected clinically prior to screening at 3 weeks of age and 55 detected clinically after 3 weeks of age having normal screens (n = 52) or never screened (n = 3). Based on data from concurrent control populations, 54.5 cases of neuroblastoma would have been expected in Quebec during the study period for an SIR of 2.17 (95% CI 1.79-2.57, P < 0.0001). For the two control groups, the overall SIR was 1.00 (NS). SIRs for Quebec by age at diagnosis in yearly intervals show a marked increased incidence under 1 year of age (SIR = 2.85, 95% CI 2.26-3.50), with no reduction in incidence in subsequent years. We conclude that screening for neuroblastoma markedly increases the incidence in infants without decreasing the incidence of unfavourable advanced stage disease in older children. It is unlikely that screening for neuroblastoma in infants will reduce the mortality of this disease.

Microsatellite instability in childhood T cell acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most frequent cancer encountered in children. Little is known about the molecular pathology of childhood T cell ALL. Oncogenesis is a multistep process that involves alterations in proto-oncogenes and tumor suppressor genes. Recently, a mutator phenotype detectable by microsatellite instabilities was shown to be associated with predisposition to cancer. This new mechanism for human carcinogenesis is caused by defects in the DNA replication/repair system. To study the involvement of some of these mutational events in the development of T cell ALL, we have initiated a systematic search for losses of heterozygosity (LOH) and microsatellite instabilities in children affected with this disease. These patients were allelotyped by PCR using 56 microsatellite markers located near known or putative tumor suppressor genes. The microsatellite patterns were altered in more than 80% of the patients. LOH were detected in chromosomes 6p, 12p and 9p. Two third of the patients were deleted for chromosome 9p21, suggesting the involvement of a tumor suppressor gene, probably the p16 gene. The only patient refractory to chemotherapy was shown to be associated with a mutator phenotype. This is the first documented case of a childhood neoplasia associated with genomic instabilities. Our results suggest that defects in DNA replication/repair components are involved in the development of a subset of childhood T cell ALL.

Cardiovascular responses to dynamic submaximal exercise in children previously treated with anthracycline

This study assessed the long-term (5-year) outcome of pediatric low-dose anthracycline therapy on the circulatory response to moderate exercise. Thirteen patients (13 +/- 4 years old) and 15 age-matched control subjects completed a maximal cycle ergometer protocol as well as two 5-minute cycling tests at 33% and 66% maximal oxygen uptake (V(O2)max) for determination of cardiac index (carbon dioxide rebreathing). V(O2)max was lower in patients than in control subjects (1.3 +/- 0.5 L/min vs 2.3 +/- 0.6 L/min) (p< 0.05). Smaller relative increases in cardiac index for similar increases in relative exercise intensities were found in patients (33% V(O2)max, 73% vs 116%; 66% V(O2)max, 115% vs 192%), as a result of smaller increases in stroke index from rest (33% V(O2)max, 33% vs 54%; 66% V(O2)max, 33% vs 69%; p< 0.05). Similarly, despite normal resting systolic function, patients exhibited a lower stroke index and higher heart rate for any given value of oxygen uptake (milliliters per minute per square meter). Children who had survived cancer exhibited stroke index impairment during exercise similar in intensity to that of recreational activities or play, attesting to a limited inotropic reserve.

A population-based study of the usefulness of screening for neuroblastoma

BACKGROUND

Neuroblastoma has many characteristics which suggest that preclinical detection might improve outcome. The Quebec Neuroblastoma Screening Project was initiated to determine whether mass screening could reduce mortality in a large cohort of infants. As an early endpoint, we report whether screening could reduce the incidence of poor-prognosis neuroblastoma in children with advanced-stage disease over 1 year of age.

METHODS

All 476,603 children born in the province of Quebec during the 5-year period of May 1, 1989, to April 30, 1994, were eligible for urinary assay of homovanillic acid and vanillylmandelic acid at 3 weeks and 6 months of age. Children with a positive screen were referred to one of four paediatric cancer centres in the province for uniform evaluation and treatment if necessary. Standardised incidence ratios (SIRs) were calculated for neuroblastoma in the province and two similar population-based controls, the state of Minnesota and the province of Ontario, during the same period of time and with similar ascertainment procedures.

FINDINGS

Compliance with screening in Quebec province was 91% at 3 weeks (n = 425,816) and 74% at 6 months (n = 349,706). Through July 31, 1995, with a follow-up of the birth cohort of 15-75 months, 118 cases of neuroblastoma were diagnosed, 43 detected preclinically by screening, 20 detected clinically before screening at 3 weeks of age, and 55 detected clinically after 3 weeks of age having normal screens (52) or never screened (3). Retrospective analysis of stored samples confirmed that 49 of 52 patients missed by screening had levels of catecholamine metabolites that were too low to be detected at 6 months or earlier. Based on US Surveillance, Epidemiology and End Results data, 54.5 cases of neuroblastoma would have been expected in Quebec province during the study period, for an SIR of 2.17 (95% CI 1.79-2.57, p < 0.0001). For the two control groups, 43 and 80 cases of neuroblastoma were detected, respectively, compared with 37.9 and 85.4 expected, overall SIR 1.00 (not significant). SIRs for Quebec province by age at diagnosis in yearly intervals show a marked increased incidence under 1 year of age (SIR 2.85, 2.26-3.50), with no reduction in incidence in subsequent years. Limiting analysis to only patients diagnosed over 1 year of age with advanced-stage disease, 22 cases were detected in Quebec province versus 14.4 expected (SIR 1.52, 0.95-2.23). Data in the two control groups show no significant increase or decrease in any-stage disease in children under or over the age of 1 year, except for an increase in early-stage disease in Minnesota children over 1 year: 10 versus 3.8 expected (SIR 2.67, 1.27-4.58).

INTERPRETATION

Screening for neuroblastoma increases the incidence in infants without decreasing the incidence of unfavourable advanced-stage disease in older children. It is unlikely that screening for neuroblastoma in infants will reduce mortality for this disease.

Cyclosporin A treatment induces overexpression of P-glycoprotein in the kidney and other tissues

To see whether P-glycoprotein (PGP) expressed in renal brush-border membranes (BBM) could interact with compounds known as modulators of multidrug resistance (MDR), photoaffinity-labeling experiments were performed. A 145k-Da protein was photolabeled with [125I] iodoarylazidoprazosin, and this labeling was reduced in the presence of cyclosporin A (CsA) and PSC-833 (PSC). Interaction of CsA with PGP was further investigated by treating rats with daily subcutaneous injections of CsA (10 mg.kg-1.day-1). After this treatment, PGP expression levels were dramatically increased in renal BBM, intestine, liver, and many other tissues except the brain. This induction was a reversible process, since after cessation of CsA administration PGP levels declined to reach values similar to those of the control groups. The increase in PGP expression in the kidney was also detected in photolabeling experiments, suggesting the induction of a functional PGP. A higher dose of CsA (50 mg/kg) given as a bolus injection did not modify PGP expression] in renal BBM. These results demonstrate that CsA induces reversible overexpression of PGP in the rat. This may present significant relevance in the design of clinical trials using CsA as a chemosensitizing agent.

Screening for neuroblastoma in North America. Preliminary results of a pathology review from the Quebec Project

BACKGROUND

The Quebec Neuroblastoma Screening Project was initiated to assess clinical and biologic aspects of neuroblastomas detected by screening infants born in the province of Quebec from May 1, 1989, to April 30, 1994.

METHODS

Infants were screened for preclinical detection of neuroblastoma by determination of catecholamine metabolites, vanillylmandelic acid (VMA), and homovanillic acid (HVA). Patients with tumors discovered through this screening as well as patients in the same birth cohort with clinically detected tumors were referred to Quebec Oncology Centers for further investigation, diagnosis, and treatment. Pathology specimens were submitted to Childrens Hospital Los Angeles for central review. Tumors were histopathologically classified according to the Shimada system.

RESULTS

As of August, 1993, 340,000 infants were screened at 3 weeks and 245,000 of them were retested at 6 months of age. Thirty-one tumors were detected through this screening and removed. Histologic material was available for 27 cases: 14 were detected at 3 weeks of age and 13 at 6 months of age. Twenty-six patients had tumors with favorable histology (FH), and one patient had a Stage I tumor with unfavorable histology (UH). At the time of this writing, all mass screening patients are alive, including one child with relapsed disease. During this period, 48 tumors were detected clinically in the same birth cohort, 40 of which were evaluated histologically. Of these 40 cases, 28 of 29 tumors diagnosed in patients up to age 12 months indicated an FH, whereas 9 of 11 tumors diagnosed in patients older than age 12 months indicated a UH. All patients with FH tumors are alive including a child with relapsed disease. The single patient with UH diagnosed before age 12 months died of disease. Of the nine patients with UH diagnosed after age 12 months, four died of disease, one relapsed, and four are alive (including one treated with bone marrow transplantation) after variable follow-up periods.

CONCLUSIONS

The tumors detected by mass screening, similar to those tumors detected through clinical examination before age 12 months, were predominantly FH with good prognosis. However, those tumors that were missed by screening and were detected clinically after the patient was 12 months of age were predominantly UH, with serious clinical problems. This subgroup of patients not detectable by the current screening system presents an immediate and important clinical challenge that should be addressed in future studies.

Interaction of drugs with P-glycoprotein in brain capillaries

P-glycoprotein (P-gp) is expressed at high levels in a variety of non-cancerous tissues such as the endothelial cells of the blood-brain barrier (BBB) capillaries. These thin capillaries tightly regulate the movement of substrates from the circulating blood into the brain. P-gp may be involved in the exclusion of various drugs from the capillary endothelial cells, blocking their entry into the brain. However, interactions of drugs with P-gp expressed in brain capillaries remain to be characterized. We have performed photoaffinity labeling studies using [125I]arylazidoprazosin (IAAP) to evaluate the inhibitory efficiency of various compounds. Cyclosporin A (CsA) and its derivative PSC 833 (PSC) were the most effective inhibitors of IAAP binding among the drugs tested. The magnitude of inhibition was: PSC > CsA > quinidine > vinblastine > verapamil < actinomycin D > colchicine > reserpine > bilirubin > doxorubicin > progesterone. Cremophor El, the vehicle used to administer CsA and PSC intravenously, was also able to inhibit IAAP photolabeling of P-gp. Labeling experiments were also performed using a photoactivatable [3H]CsA derivative. Photolabeling of P-gp with this compound was abolished almost completely by CsA and PSC. In vivo studies were also performed by treating rats with CsA [10 mg/(kg.day) for 10 days]. Following this treatment, no alteration in the level of P-gp expression in brain capillaries was observed. These results suggest that, at the proper dosage, administration of CsA to cancer patients could help to enhance the response of brain tumors to chemotherapeutic agents without modifying the intrinsic level of P-gp expression in this tissue.

High frequency of germline p53 mutations in childhood adrenocortical cancer

BACKGROUND

Adrenocortical carcinoma (ADCC) is a rare childhood cancer, affecting three of 1 million children younger than 16 years old in the United States. ADCC may be found in association with the Li-Fraumeni and Beckwith-Wiedemann syndromes. Children with ADCC are also at substantially increased risk of second primary cancers. Because of these associations, it is believed that the genetic basis for ADCC is stronger than for most childhood malignancies. Germline mutations of the TP53 tumor suppressor gene are associated with cancer predisposition in families with the Li-Fraumeni syndrome as well as in individuals with sporadically occurring component tumors of the syndrome.

PURPOSE

We investigated the possibility that germline TP53 gene alterations existed in children with ADCC.

METHODS

Sixteen children with ADCC under the age of 18 were identified from searches of medial oncology records at three Canadian hospitals. Eleven of these 16 patients identified were alive. The mean age at diagnosis was 4.8 years (range, 1-17 years). Family histories were obtained for 11 unselected children with ADCC (six girls and five boys). Pathologic confirmation of tumor diagnosis was obtained from the medical records. Using single-strand conformational polymorphism analysis followed by single-strand DNA sequencing, genomic DNA extracted from whole blood was analyzed for the presence of TP53 mutations for six living ADCC patients.

RESULTS

Three of six (50%) children were found to carry germline TP53 mutations in exons 5, 6, and 7, respectively. Both wild-type and mutant alleles were identified in all three TP53 sequences, indicating that the patients were heterozygous for germline TP53 mutations. None of these children was from a family with the Li-Fraumeni syndrome. The mutation in one child was shown to be inherited from the mother, who subsequently developed breast cancer. A striking excess of cancer was found in one family of a patient carrying wild-type TP53.

CONCLUSIONS

Our observation of a high frequency of germline TP53 mutations in children with sporadic ADCC suggests that these children may represent probands with which to ascertain Li-Fraumeni syndrome families. It may be reasonable for children with adrenocortical carcinoma to be candidates for germline TP53 analysis. In light of the wealth of information in the Li-Fraumeni literature that associates germline TP53 mutations with a variety of malignancies, this testing may have important consequences for risk assessment for other close relatives, including early-onset breast cancer in the mothers.

Measurement of nucleoside diphosphate kinase-Nm23 activity by anion-exchange high-performance liquid chromatography

A first-order assay to detect the activity of nucleoside diphosphate kinase (NDP-kinase; EC 2.7.4.6) was developed. In this assay, the activity of NDP-kinase is measured using various deoxy- and ribonucleotide triphosphates as phosphate donors and dADP as phosphate acceptor. The enzyme activity is determined by quantifying, after anion-exchange HPLC, the amount of newly synthesized dATP. Contrary to the most common coupled enzymic assays or isotopic assays the use of different donor-acceptor pairs is not restricted. The resolution of the procedure described is limited only by the chromatographic separation of substrate and product pairs participating in the reaction.

[10 years of medical-hospital data processing. Returns, answers, hazards or benefits of technology serving mankind]

The medical data processing has been introduced 10 years ago in the city hospital of Neuchâtel. The application includes a problem oriented electronic medical record, software assistance for diagnoses coding, diagnostic and therapeutic files, access to Medline, specific applications for intensive care and neonatology, and also a medical server meant for exchanging data with general practitioners and other hospitals. The reliability, the security and the usefulness of the application are discussed, as well as the orientation of the new application, being developed at present, is described. The physicians, i.e. today users, must prepare themselves the applications for the coming years. The treatment of the medical data must be optimal and also make the personal relationship between the physician and his patient easier.

Absence of p53 gene mutations in primary neuroblastomas

Neuroblastoma is a common childhood malignancy of the sympathetic nervous system. Mutations in p53, a tumor suppressor gene located on the short arm of chromosome 17, are one of the most common genetic lesions in human cancers. The evidence for trisomies of 17q with loss of 17p in some cases of neuroblastoma led us to consider whether p53 mutations might contribute to the onset and progression of this malignancy. In this study, primary tumors from 38 neuroblastoma patients were screened for mutations within the coding exons of the p53 gene by single-strand conformation polymorphism analysis, and potential mutations were further analyzed by nucleotide sequence analysis. Previously described sequence variations were detected in many of the tumors, including a silent polymorphism at codon 213 (CGA to CGG) and the nontransforming Pro to Arg substitution at codon 72 (CCC to CGC). However, no other sequence variations were detected within the coding portions of the p53 gene. This finding suggests that p53 mutations do not contribute to the etiology of neuroblastoma and that the chromosome 17 alterations observed in neuroblastoma involve genes which are distinct from the p53 locus.

Circadian time-dependent response of childhood lymphoblastic leukemia to chemotherapy: a long-term follow-up study of survival

The evolution of 118 children treated for acute lymphoblastic leukemia between 1976 and 1984, and followed until 1991, was reviewed. Maintenance chemotherapy consisted of daily 6-mercaptopurine (6-MP), weekly methotrexate (MTX), and monthly vincristine and prednisone. Eighty-two children took 6-MP and MTX in the morning, and 36 took them in the evening. Disease-free survival, as determined by Kaplan-Meier analysis, was better for children on evening chemotherapy. Regression analysis (Cox proportional hazards model, with evening versus morning schedule as exposure variable, and age at diagnosis, leucocytosis at diagnosis, and sex as covariates) showed that for those surviving free of disease for longer than 78 weeks, the risk of relapse was 2.56 times greater for the morning schedule than for the evening one.

Screening for neuroblastoma in North America. 2-year results from the Quebec Project

The Quebec Neuroblastoma Screening Project was initiated to assess the clinical and biological aspects of screening infants for the presence of neuroblastoma in North America. All children born in the province of Quebec from May 1, 1989 to April 30, 1994 are eligible for participation. This report provides results from 22 months' accrual of infants who were screened using urine-saturated filter paper for determination of the catecholamine metabolites vanillylmandelic acid (VMA) and homovanillic acid (HVA). More than 157,000 infants have been screened to date at 3 weeks of age, representing 92% of the entire birth population of Quebec. Over 98,000 infants have been screened a second time at 6 months of age, which made up 76% of the Quebec birth cohort. After a two-stage initial screening, 340 (0.13%) infants (182 at 3 weeks and 158 at 6 months) required second laboratory examinations because of elevated levels of urinary VMA, HVA, or both. Twenty infants from the 3-week screening (0.01%) and nine from the 6-month screening (0.01%) were subsequently referred to one of four Quebec pediatric oncology centers for neuroblastoma evaluation. Seven of 20 children from the 3-week screening and two of nine children from the 6-month screening have been identified as having neuroblastoma. During the same period, 14 additional children in the birth cohort were diagnosed clinically with neuroblastoma; eight were diagnosed prior to screening at 3 weeks of age, three children had negative results at 3 weeks of age, two had negative results at 3 weeks and at 6 months of age, and one had never been screened.(ABSTRACT TRUNCATED AT 250 WORDS)

A population-based study of neuroblastoma incidence, survival, and mortality in North America

PURPOSE

The purpose of this study was twofold: (1) to provide a population-based estimate of neuroblastoma incidence, disease stage and age distribution, and survival and mortality rates in North America; and (2) to compare these figures in the province of Quebec at a time shortly before the institution of province-wide screening with those in a population-based control group, the Greater Delaware Valley (GDV) Pediatric Tumor Registry.

MATERIALS AND METHODS

In Quebec, the four major pediatric teaching hospital records were searched for children with a diagnosis of neuroblastoma. Tumor board registry data and information supplied to the Division of Vital Statistics were also reviewed. Birth statistics were obtained from the population registry. The GDV Pediatric Tumor Registry is a population-based registry of pediatric cancer covering all of Delaware and parts of New Jersey, Pennsylvania, and Maryland. Age, stage of disease, and follow-up data were obtained through December 31, 1989, with Evans neuroblastoma staging data used for all comparisons.

RESULTS

One hundred thirty children with neuroblastoma were identified in Quebec and 165 in the GDV, in a combined population of 3,178,736 children. The annual incidence of neuroblastoma was 10.95/10(6) under the age of 15 years and 27.75/10(6) between the ages of 0 and 4 years. The annual mortality rate due to neuroblastoma was 4.89/10(6) and 9.10/10(6) for the age groups 0 to 14 and 0 to 4, respectively. The overall 10-year survival rate for the 295 cases of neuroblastoma was 55%. The 10-year survival rates for patients with Evans stage I-IV and IVS disease were 88%, 90%, 63%, 21%, and 81%. There was no significant difference observed in the incidence, mortality, or survival in the two populations.

CONCLUSION

These data represent the first large, population-based description of the clinical presentation and outcome of patients with neuroblastoma in North America, with no significant differences noted between Quebec patients and the GDV patients.

Isolation of 6-mercaptopurine in human plasma by aluminum ion complexation for high-performance liquid chromatographic analysis

A sample preparation technique and a high-performance liquid chromatographic method for 6-mercaptopurine (6-MP) that is simple, sensitive and without interference from its metabolites is described. 6-Thioguanine (6-TG) is added as an internal standard to the plasma sample, which is then treated with an aqueous solution of aluminum perchlorate to denature the plasma proteins and form complexes with 6-TG, 6-MP and its major metabolite, 6-thiouric acid (6-TUA). These complexes coprecipitate with proteins on centrifugation. 6-MP and its analogues are then extracted from the precipitate with perchloric acid containing sodium hydrosulfite and the extract is chromatographed on an Ultrasphere ODS column eluted with 0.1 M phosphoric acid and 0.001 M dithiothreitol in deionized water. The eluate is monitored at 340 nm. No interfering peak was encountered in over 300 clinical plasma samples. 6-TUA was separated from 6-MP and was found to be present in much higher concentration than 6-MP itself throughout the sampling time (6 h) following oral administration of the drug.

Epstein-Barr virus polymorphic B-cell lymphoma associated with leukemia and with congenital immunodeficiencies

Polymorphic B-cell lymphoma seen in four patients with congenital immunodeficiencies and in two patients with leukemia receiving chemotherapy was associated with the Epstein-Barr virus (EBV). The tumors had characteristic histologic features: they were polymorphic consisting of a mixture of lymphoblasts and differentiated cells including plasma cells, and areas of hemorrhagic necrosis were prominent. The tumors were either polyclonal, monoclonal, or multiclonal. Patients with congenital immunodeficiencies who developed these tumors died despite radiotherapy, corticosteroids plus acyclovir, or a combination of intravenous (IV) immunoglobulins and alpha 2 interferon. Patients with leukemia recovered when immunosuppressive drugs were discontinued and leukemia has not recurred over a period of 2 and 4 years, respectively, in the two patients.

5-azacytidine and 5-azadeoxycytidine inhibit human immunodeficiency virus type 1 replication in vitro

Chemotherapeutic agents which affect the integration, stability, or inducibility of the human immunodeficiency virus (HIV) provirus would have considerable value in treating acquired immunodeficiency syndrome. Two nucleoside analogs of cytosine, 5-azacytidine and 5-azadeoxycytidine, which seem to have such value because of their capabilities to affect both the stability and the methylation patterns of the nucleic acids into which they are incorporated, were tested for their ability to inhibit the replication of HIV type 1 (HIV-1) in human CEM T cells in vitro. 5-Azadeoxycytidine (1 microM) completely inhibited HIV replication in CEM cells, by the criteria of reduced viral antigen expression and decreased supernatant reverse transcriptase activity, with little toxicity for the treated cells. 5-azacytidine (1 microM) also inhibited HIV replication, but less effectively. When added 2 or more h after CEM cells were infected with HIV-1, both 5-azacytosine derivatives were less effective than they were when added at the time of infection. Even 2 h of exposure to 5-azadeoxycytidine was sufficient for inhibition of HIV replication. Although long exposure to either analog at concentrations of 1 microM would result in pronounced cellular cytotoxicity, the the fact that short exposures to the same dose of drug inhibit HIV replication but are not toxic for the cells implies that cellular toxicity itself is not an important mechanism of the antiviral action of the analogs.

High-performance liquid chromatographic determination of mitoxantrone in plasma utilizing non-bonded silica gel for solid-phase isolation to reduce adsorptive losses on glass during sample preparation

Mitoxantrone, a highly active antineoplastic agent, was found to bind strongly to non-bonded silica gel and glassware. When a Hamilton syringe was used to load and inject a mitoxantrone solution (0.4 microgram/ml in water) on to a high-performance liquid chromatographic (HPLC) system, about 95% of the loaded compound was found to bind to the glass surface of the syringe barrel and could not be removed by rinsing with water. It could, however, be removed slowly with an acidic solution and thus a small peak of mitoxantrone was present on the chromatogram whenever a blank acidic solution was injected with the syringe. The bound mitoxantrone could be removed effectively from the syringe surface with a solution of tetramethylammonium chloride, citric acid, methanol and water (elution solvent). This binding introduces a large error in assay results and might be one of the major factors responsible for contradictory pharmacokinetic data that have been reported. A new plasma preparation scheme and an HPLC method for mitoxantrone were developed to address this binding problem. Mitoxantrone was extracted directly from plasma samples with a plastic mini-column packed with non-bonded silica gel and eluted with the above elution solvent. The eluent was analysed by HPLC on an ODS column with an absorbance detector at 658 nm. The mobile phase was 0.1 M triethylamine phosphate (pH 3.0) in water-tetrahydrofuran-methanol (69:1:30) containing 0.02 M tetramethylammonium chloride. Methylene blue was added as an internal standard. Preliminary results showed that mitoxantrone levels in human plasma followed a triphasic decay curve after an intravenous bolus injection. The terminal elimination half-lives measured in three patients (mean t1/2 gamma = 25 min) were all shorter than the published values which ranged from 56 min to 9 days.

Inhibition of DNA polymerase-alpha by ara-CMP in the presence of a regulatory protein extracted from human promyelocytic leukemic cells (HL-60)

Cytotoxicity of arabinofuranosylcytosine (ara-C) has been related in vitro to the inhibition of the DNA polymerase activities by arabinosylcytosine triphosphate (ara-CTP) and the incorporation of ara-C into the DNA where, acting as a chain terminator, it slows the chain elongation. Induced in vitro cellular resistance to ara-C was shown to be secondary to altered deoxycytidine (dCyd) kinase activity, dCyd deaminase activity, or deoxynucleotides triphosphates (dNTP) pools. Recent studies reported no differences of ara-C metabolism in cells obtained from leukemic patients at diagnosis and at relapse after ara-C therapy, suggesting that unknown cellular biochemical determinants may be involved in acquisition of ara-C resistance. Using dialysed crude extracts of leukemic cells obtained from patients at diagnosis, we observed variable inhibition of their DNA polymerase activities by arabinosylcytosine monophosphate (ara-CMP) at 2 mmol/L (0% to 50% inhibition). In similar conditions, ara-CMP reduced the polymerase activities of human thymus extract by 35% and 55% in extract of HL-60 cells (cultured human promyelocytic cells). The ara-CMP factor responsible for inhibition of DNA polymerase activity was nondialysable, heat labile, proteinase K sensitive, and has an estimated molecular mass of 30 kilodalton by gel filtration. After partial purification, this protein had no DNA polymerase RNA polymerase activities. In presence of the regulator and ara-CMP at 2 mmol/L, we observed no inhibition of the HL-60 3'----5' and 5'----3' exonucleases activities, suggesting the regulator interaction being mainly with the DNA polymerases in presence of ara-CMP. The relevance of the presence or absence of this protein regarding the cell sensitivity to ara-C is under investigation.

Effect of the interval between exposures to cytarabine on its cytotoxic action on HL-60 myeloid leukemic cells

As an in vitro model for the chemotherapy of acute myeloid leukemia with cytarabine (ARA-C), the cytotoxicity of this drug was investigated using a human promyelocytic cell line (HL-60) and different drug schedules. The continuous exposure to ARA-C was shown to be more cytotoxic than the intermittent exposures at identical concentrations or under conditions where the concentrations multiplied by time of exposure were the same. In a comparison of exposures, as the intervals between drug exposures were reduced, the cytotoxicity of ARA-C increased. Flow microfluorometric analysis of DNA content showed that a 3-hour exposure to ARA-C every 6 hours produced a greater accumulation of cells in S phase than the same exposure repeated every 12 hours. After a 3-hour exposure to 20 micrograms/ml of ARA-C, the cells recovered 38% and 85% of their capacity to synthesize DNA within 4 and 8 hours, respectively. These findings can be explained in part by the short half-life of the intracellular nucleotide pool of ARA-CTP in these cells (about 60 minutes). These data indicate that when there is a prolongation of the interval between exposures to ARA-C, a greater fraction of cells recover from the inhibitory effects of this drug and escape its cytotoxic action. These observations may be important with respect to the design of more optimal schedules of high-dose ARA-C therapy for the treatment of patients with acute leukemia.