Being certain even when you're wrong: heuristics and thin slicing in haematopoietic cell transplantation

The role of randomized controlled trials, registries, observational databases in evaluating new interventions

Approaches to comparing safety and efficacy of interventions include analyzing data from randomized controlled trials (RCTs), registries and observational databases (ODBs). RCTs are regarded as the gold standard but data from such trials are sometimes unavailable because a disease is uncommon, because the intervention is uncommon, because of structural limitations or because randomization cannot be done for practical or (seemingly) ethical reasons. There are many examples of an unproved intervention being so widely-believed to be effective that clinical trialists and potential subjects decline randomization. Often, when a RCT is finally done the intervention is proved ineffective or even harmful. These situations are termed medical reversals and are not uncommon [1,2]. There is also the dilemma of when seemingly similar RCTs report discordant conclisions Data from high-quality registries, especially ODBs can be used when data from RCTs are unavailable but also have limitations. Biases and confounding co-variates may be unknown, difficult or impossible to identify and/or difficult to adjust for adequately. However, ODBs sometimes have large numbers of diverse subjects and often give answers more useful to clinicians than RCTs. Side-by-side comparisons suggest analyses from high-quality ODBs often give similar conclusions from high quality RCTs. Meta-analyses combining data from RCTs, registries and ODBs are sometimes appropriate. We suggest increased use of registries and ODBs to compare efficacy of interventions.

What Causes Aplastic Anaemia: Results of Transplants from Genetically-Identical Twins

Background

Aplastic anaemia has diverse aetiologies. Distinguishing between these is, in part, testable by analyzing results of haematopoietic cells transplants between genetically-identical twins one of whom has aplastic anaemia.

Objective

Describe outcomes of genetically-identical twin transplants for aplastic anaemia with and without pretransplant conditioning.

Methods

We interrogated data from an observational database of 59 consecutive recipients of genetically-identical twin transplants for aplastic anaemia reported to the Center for International Blood and Marrow Transplant Research (CIBMTR) 2000-2019.

Results

38 subjects were male. Median age was 18 years (Interquartile Range [IQR], 11-32 years). Median interval from diagnosis to transplant was 2 months (IQR 1-3 months). 11 subjects received a 1st transplant without pretransplant conditioning. 2 of recovered normal bone marrow function. The other 9 received a 2nd transplant with pretransplant conditioning 7 of whom recovered. 48 subjects received pretransplant conditioning before a 1st or 2nd transplant all of whom recovered.

Conclusion

Only some genetically-identical twins with aplastic anaemia recover normal bone marrow function after a 1st haematopoietic cell transplant without pretransplant conditioning whereas most subjects recover when a transplant is preceded by pretransplant conditioning. These data are consistent with an immune-mediated aetiology of aplastic anaemia in most cases.

Will New Drugs Replace Transplants for Chronic Lymphocytic Leukaemia?

Transplants have been used to treat chronic lymphocytic leukemia (CLL) for more than 35 years. Use has been restricted to <1 percent of highly selected persons typically failing concurrent conventional therapies. As therapies of CLL have evolved, so have indications for transplantation and transplant techniques. The data that we review indicate that transplants can result in long-term leukemia-free survival in some persons but are associated with substantial transplant-related morbidity and mortality. We discuss the mechanisms underlying the anti-leukemia effects of transplants including drugs, ionizing radiations, immune-mediated mechanisms and/or a combination. We discuss prognostic and predicative covariates for transplant outcomes. Importantly, we consider whether there is presently a role of transplants in CLL and who, if anyone, is an appropriate candidate in the context of new drugs.

Is there a role for haematopoietic cell transplants after radiation and nuclear accidents?

My task is to consider whether haematopoietic cell transplants would be considered appropriate today in persons with features like victims of high-dose and dose-rate ionizing radiations after the Chernobyl nuclear power facility accident in 1986 given knowledge and experience gained over the past 35 years. First I consider the conceptual bases for considering an intervention appropriate and then the metric for deciding whether a transplant is appropriate in similar persons. Data needed to support this decision-making process include estimates of dose, dose-rate, dose uniformity, synchronous or metachronous injuries, donor availability and alternative interventions. Many of these co-variates have substantial uncertainties. Fundamental is a consideration of potential benefit-to-risk and risk-to-benefit ratios under conditions of substantial inaccuracy and imprecision. The bottom line is probably fewer transplants would be done and more victims would receive molecularly-cloned haematopoietic growth factors.