A Bayesian quantile joint modeling of multivariate longitudinal and time-to-event data

Linear mixed models are traditionally used for jointly modeling (multivariate) longitudinal outcomes and event-time(s). However, when the outcomes are non-Gaussian a quantile regression model is more appropriate. In addition, in the presence of some time-varying covariates, it might be of interest to see how the effects of different covariates vary from one quantile level (of outcomes) to the other, and consequently how the event-time changes across different quantiles. For such analyses linear quantile mixed models can be used, and an efficient computational algorithm can be developed. We analyze a dataset from the Acute Lymphocytic Leukemia (ALL) maintenance study conducted by Tata Medical Center, Kolkata. In this study, the patients suffering from ALL were treated with two standard drugs (6MP and MTx) for the first two years, and three biomarkers (e.g. lymphocyte count, neutrophil count and platelet count) were longitudinally measured. After treatment the patients were followed nearly for the next three years, and the relapse-time (if any) for each patient was recorded. For this dataset we develop a Bayesian quantile joint model for the three longitudinal biomarkers and time-to-relapse. We consider an Asymmetric Laplace Distribution (ALD) for each outcome, and exploit the mixture representation of the ALD for developing a Gibbs sampler algorithm to estimate the regression coefficients. Our proposed model allows different quantile levels for different biomarkers, but still simultaneously estimates the regression coefficients corresponding to a particular quantile combination. We infer that a higher lymphocyte count accelerates the chance of a relapse while a higher neutrophil count and a higher platelet count (jointly) reduce it. Also, we infer that across (almost) all quantiles 6MP reduces the lymphocyte count, while MTx increases the neutrophil count. Simulation studies are performed to assess the effectiveness of the proposed approach.

Relapsed Acute Lymphoblastic Leukemia

Outcomes for children with acute lymphoblastic leukemia (ALL) have improved worldwide to >85%. For those who relapse, outcomes have remained static at ~50% making relapsed acute lymphoblastic leukemia one of the leading causes of death in childhood cancers. Those relapsing within 18 mo in the bone marrow have a particularly dismal outcome. The mainstay of treatment is chemotherapy, local radiotherapy with or without hematopoietic stem cell transplantation (HSCT). Improved biological understanding of mechanisms of relapse and drug resistance, use of innovative strategies to identify the most effective and least toxic treatment regimens and global partnerships are needed to improve outcomes in these patients. Over the last decade, new therapeutic options and strategies have been developed for relapsed ALL including immunotherapies and cellular therapies. It is imperative to understand how and when to use these newer approaches in relapsed ALL. Increasingly, integrated precision oncology strategies are being used to individualize treatment of patients with relapsed ALL, especially in patients with poor response disease.

A Bayesian joint model for multivariate longitudinal and time-to-event data with application to ALL maintenance studies

The most common type of cancer diagnosed among children is the Acute Lymphocytic Leukemia (ALL). A study was conducted by Tata Translational Cancer Research Center (TTCRC) Kolkata, in which 236 children (diagnosed as ALL patients) were treated for the first two years (approximately) with two standard drugs (6MP and MTx) and were then followed nearly for the next 3 years. The goal is to identify the longitudinal biomarkers that are associated with time-to-relapse, and also to assess the effectiveness of the drugs. We develop a Bayesian joint model in which a linear mixed model is used to jointly model three biomarkers (i.e. white blood cell count, neutrophil count, and platelet count) and a semi-parametric proportional hazards model is used to model the time-to-relapse. Our proposed joint model can assess the effects of different covariates on the progression of the biomarkers, and the effects of the biomarkers (and the covariates) on time-to-relapse. In addition, the proposed joint model can impute the missing longitudinal biomarkers efficiently. Our analysis shows that the white blood cell (WBC) count is not associated with time-to-relapse, but the neutrophil count and the platelet count are significantly associated with it. We also infer that a lower dose of 6MP and a higher dose of MTx jointly result in a lower relapse probability in the follow-up period. Interestingly, we find that relapse probability is the lowest for the patients classified into the "high-risk" group at presentation. The effectiveness of the proposed joint model is assessed through the extensive simulation studies.

Maintenance Treatment in Acute Lymphoblastic Leukemia: A Clinical Primer

Cure rates in pediatric acute lymphoblastic leukemia (ALL) currently approach 90% in the developed world. Treatment involves 6-8 mo of intensive multi-drug chemotherapy followed by 24 mo of maintenance treatment (ALL-MT). The cornerstone of ALL-MT is the daily administration of oral 6-mercaptopurine (6MP), a purine analogue. 6MP is combined with weekly oral methotrexate (MTX), an antifolate drug, to augment therapeutic activity. Some protocols include additional chemotherapy drugs (such as vincristine and corticosteroids) during MT. The objective of ALL-MT is to ensure uninterrupted treatment at the highest tolerated doses of 6MP and MTX. This requires periodic adjustments of 6MP and MTX doses throughout treatment. Tolerance is determined through regular clinical assessments and careful monitoring of blood counts. Tolerated drug doses vary widely among patients, influenced by genetic and non-genetic factors, and require individualized dosing. Suboptimal treatment intensity in ALL-MT is associated with inferior outcomes and results from failure to treat at highest tolerated drug doses and/or interruptions in treatment due to non-adherence or toxicity. Management of MT thus requires close supervision to ensure treatment adherence, periodic drug dose modifications, and treatment to tolerance, while minimizing treatment interruptions due to toxicity. The review highlights these challenges and discusses approaches and strategies for the management of MT, focusing on the Indian context.

Comparative treatment costs of risk-stratified therapy for childhood acute lymphoblastic leukemia in India

BACKGROUND

To evaluate the treatment cost and cost effectiveness of a risk-stratified therapy to treat pediatric acute lymphoblastic leukemia (ALL) in India.

METHODS

The cost of total treatment duration was calculated for a retrospective cohort of ALL children treated at a tertiary care facility. Children were risk stratified into standard (SR), intermediate (IR) and high (HR) for B-cell precursor ALL, and T-ALL. Cost of therapy was obtained from the hospital electronic billing systems and details of outpatient (OP) and inpatient (IP) from electronic medical records. Cost effectiveness was calculated in disability-adjusted life years.

RESULTS

One hundred and forty five patients, SR (50), IR (36), HR (39), and T-ALL (20) were analyzed. Median cost of the entire treatment for SR, IR, HR, and T-ALL was found to be $3900, $5500, $7400, and $8700, respectively, with chemotherapy contributing to 25%-35% of total cost. Out-patient costs were significantly lower for SR (p < 0.0001). OP costs were higher than in-patient costs for SR and IR, while in-patient costs were higher in T-ALL. Costs for non-therapy admissions were significantly higher in HR and T-ALL (p < 0.0001), representing over 50% of costs of in-patient therapy. HR and T-ALL also had longer durations of non-therapy admissions. Based on WHO-CHOICE guidelines, the risk-stratified approach was very cost effective for all categories of patients.

CONCLUSIONS

Risk-stratified approach to treat childhood ALL is very cost-effective for all categories in our setting. The cost for SR and IR patients is significantly reduced through decreased IP admissions for both, chemotherapy and non-chemotherapy reasons.

Activity and toxicity of intramuscular 1000 iu/m2 polyethylene glycol-E. coli L-asparaginase in the UKALL 2003 and UKALL 2011 clinical trials

In successive UK clinical trials (UKALL 2003, UKALL 2011) for paediatric acute lymphoblastic leukaemia (ALL), polyethylene glycol‐conjugated E. coli L‐asparaginase (PEG‐EcASNase) 1000 iu/m² was administered intramuscularly with risk‐stratified treatment. In induction, patients received two PEG‐EcASNase doses, 14 days apart. Post‐induction, non‐high‐risk patients (Regimens A, B) received 1–2 doses in delayed intensification (DI) while high‐risk Regimen C patients received 6–10 PEG‐EcASNase doses, including two in DI. Trial substudies monitored asparaginase (ASNase) activity, ASNase‐related toxicity and ASNase‐associated antibodies (total, 1112 patients). Median (interquartile range) trough plasma ASNase activity (14 ± 2 days post dose) following first and second induction doses and first DI dose was respectively 217 iu/l (144–307 iu/l), 265 iu/l (165–401 iu/l) and 292 iu/l (194–386 iu/l); 15% (138/910) samples showed subthreshold ASNase activity (<100 iu/l) at any trough time point. Older age was associated with lower (regression coefficient −9.5; p < 0.0001) and DI time point with higher ASNase activity (regression coefficient 29.9; p < 0.0001). Clinical hypersensitivity was observed in 3.8% (UKALL 2003) and 6% (UKALL 2011) of patients, and in 90% or more in Regimen C. A 7% (10/149) silent inactivation rate was observed in UKALL 2003. PEG‐EcASNase schedule in UKALL paediatric trials is associated with low toxicity but wide interpatient variability. Therapeutic drug monitoring potentially permits optimisation through individualised asparaginase dosing.

Unsatisfactory quality of E. coli asparaginase biogenerics in India: Implications for clinical outcomes in acute lymphoblastic leukaemia

BACKGROUND

The biotherapeutic asparaginase is a cornerstone of therapy in acute lymphoblastic leukaemia (ALL). With limited access to the original native Escherichia coli-derived asparaginase (EcASNase), a variety of EcASNase biogenerics are used in low-middle-income countries (LMICs). The variable quality of these biogenerics potentially influences clinical outcomes.

PROCEDURE

Seven biogeneric EcASNases (P1-P7) marketed widely in India were evaluated, with P2 as an exemplar for in vivo monitoring. Therapeutic activity of P2 (10,000 IU/m² /dose, intramuscular, every 72 hours) was monitored during induction therapy, and drug-related toxicities recorded. Molecular identity, purity and in vitro drug activity of seven biogenerics were characterised using multimodal analyses, and findings compared with reference EcASNase (R).

RESULTS

In patients (N = 62) receiving P2, subtherapeutic asparaginase activity (<100 U/L) was observed in 66% (46/70) of trough timepoints (72 hours postdose) during induction. Twelve patients (19%), 11 with high-risk ALL, developed hypersensitivity. Isoforms of EcASNase were identified in all seven biogenerics. All generic products contained impurities with batch-to-batch variability. These included high levels of protein aggregates and host cell protein contamination. In vitro assays of EcASNase activity and leukaemia cell line cytotoxicity were not discriminatory.

CONCLUSIONS

Our findings confirm widespread concerns over the unsatisfactory quality and therapeutic activity of native EcASNase biogenerics marketed in LMICs. Appropriate use of these products requires monitored studies to identify clinical suitability and determine appropriate dosing and schedule. For large parts of the world, assured access to high-quality asparaginases remains an unmet therapeutic need.

Foetal growth parameters--clinical versus ultrasonographic

The study was conducted in 2831 pregnant women with no diagnosed complication at the time of registration to obtain normal foetal growth pattern for clinical and ultrasonographic parameters. Normal values for maternal weight, fundal height and abdominal girth for clinical and biparietal diameter, abdominal circumferences and femoral length for ultrasonographic parameters are presented. Clinical and ultrasonographic parameters were compared for their efficacy in prediction of low birth weight. Neither clinical nor ultrasonographic parameters were found to be satisfactory in identifying the foetus at risk of low birth weight. It has been found that clinical parameters for routine monitoring are as effective as ultrasonographic parameters and have the added advantage of being easily replicable at the peripheral level of health care.

Randomized clinical trial with intrauterine devices (levonorgestrel intrauterine device (LNG), CuT 380Ag, CuT 220C and CuT 200B). A 36-month study. Indian Council of Medical Research Task Force on IUD

A total of 1905 subjects were randomly allocated to four types of intrauterine devices (IUDs) and were observed for 45,683 woman-months of use. While no method failure was observed with levonorgestrel (LNG) IUD, 11 women became pregnant with other devices; 4 with Copper T 380Ag, 1 with Copper T 220C, and 6 while using Copper T 200B, indicating method failure rates of 1.0, 0.3 and 1.6, respectively, at 36 months of use. These rates were within acceptable range. Continuation rates were significantly lower with LNG IUD (74.5, 58.7, 38.8 at 1 year, 2 years and 3 years, respectively) as compared to other copper devices, which ranged between 82.4 to 84.4 at 1 year, 66.6 to 69.9 at 2 years and 45.4 to 50.4 at 3 years. The difference in continuation rates was mainly due to menstrual disturbances (e.g. amenorrhoea, irregular bleeding) which were higher with LNG IUD (27.9 per 100 users) as compared to the copper devices (13.4-15.4 per 100 users) at 36 months of use. The risk of expulsion ranged between 8.3 to 10.6 per 100 users and was comparable for all the devices. The observations from the present study based on 36 months of experience with different intrauterine devices do not indicate the need to replace CuT 200, the device currently in use in the National Programme.

Comparative evaluation of contraceptive efficacy of norethisterone oenanthate (200 mg) injectable contraceptive given every two or three monthly. Indian Council of Medical Research Task Force on Hormonal Contraception

A total of 2388 subjects, 1181 for 60 +/- 5-day and 1207 for 90 +/- 5-day treatment regimen with norethisterone oenanthate (NET OEN) 200 mg injection, were observed for 24 months, constituting 28,513 woman-months. This clinical trial represents the largest clinical trial undertaken on NET OEN. The observations indicated that NET OEN given at 60 +/- 5-day intervals provides adequate contraceptive protection. However, as compared to the published studies elsewhere, higher method failures were seen during the first six months of NET OEN usage, when all women were receiving the drug at 60 +/- 5-day intervals. The reasons for this discrepant observation in the present study cannot be explained. The higher method failures reported with 90 +/- 5-day regimen were mainly during the third month following the injection, suggesting reduced contraceptive efficacy of the drug during this period. Thin build women (body weight less than or equal to 40 kg) were at higher risk of involuntary pregnancy. Disrupted menstrual pattern was the major reason for discontinuation ranging between 42-43 per 100 users at the end of 24 months. Amongst these, amenorrhoea was the commonest reason for discontinuation. No change in blood pressure was observed during contraceptive usage. The majority of NET OEN users did not show any change in body weight. The overall continuation rates with NET OEN were lower than those observed in similar conditions with Cu-T 200 mm2 IUCD.