formaldehyde and acute myeloid leukemia (AML)

INTRODUCTION

Causal epidemiology for regulatory risk analysis seeks to evaluate how removing or reducing exposures would change disease occurrence rates. We define interventional probability of causation (IPoC) as the change in probability of a disease (or other harm) occurring over a lifetime or other specified time interval that would be caused by a specified change in exposure, as predicted by a fully specified causal model. We define the closely related concept of causal assigned share (CAS) as the predicted fraction of disease risk that would be removed or prevented by a specified reduction in exposure, holding other variables fixed. Traditional approaches used to evaluate the preventable risk implications of epidemiological associations, including population attributable fraction (PAF) and the Bradford Hill considerations, cannot reveal whether removing a risk factor would reduce disease incidence. We argue that modern formal causal models coupled with causal artificial intelligence (CAI) and realistically partial and imperfect knowledge of underlying disease mechanisms, show great promise for determining and quantifying IPoC and CAS for exposures and diseases of practical interest.

METHODS

We briefly review key CAI concepts and terms and then apply them to define IPoC and CAS. We present steps to quantify IPoC using a fully specified causal Bayesian network (BN) model. Useful bounds for quantitative IPoC and CAS calculations are derived for a two-stage clonal expansion (TSCE) model for carcinogenesis and illustrated by applying them to benzene and formaldehyde based on available epidemiological and partial mechanistic evidence.

RESULTS

Causal BN models for benzene and risk of acute myeloid leukemia (AML) incorporating mechanistic, toxicological and epidemiological findings show that prolonged high-intensity exposure to benzene can increase risk of AML (IPoC of up to 7e-5, CAS of up to 54%). By contrast, no causal pathway leading from formaldehyde exposure to increased risk of AML was identified, consistent with much previous mechanistic, toxicological and epidemiological evidence; therefore, the IPoC and CAS for formaldehyde-induced AML are likely to be zero.

CONCLUSION

We conclude that the IPoC approach can differentiate between likely and unlikely causal factors and can provide useful upper bounds for IPoC and CAS for some exposures and diseases of practical importance. For causal factors, IPoC can help to estimate the quantitative impacts on health risks of reducing exposures, even in situations where mechanistic evidence is realistically incomplete and individual-level exposure-response parameters are uncertain. This illustrates the strength that can be gained for causal inference by using causal models to generate testable hypotheses and then obtaining toxicological data to test the hypotheses implied by the models-and, where necessary, refine the models. This virtuous cycle provides additional insight into causal determinations that may not be available from weight-of-evidence considerations alone.

The relationship of the clinicopathological characteristics and treatment results of post-Chornobyl papillary thyroid microcarcinomas with the latency period and radiation exposure

INTRODUCTION

A worldwide increase in the incidence of thyroid cancer during the last decades is largely due to papillary thyroid microcarcinomas (MPTCs), which are mostly low-risk tumors. In view of recent clinical recommendations to reduce the extent of surgery for low-risk thyroid cancer, and persisting uncertainty about the impact of radiation history, we set out to address whether clinicopathological characteristics and prognosis of post-Chornobyl MPTCs were changing with regard to: i) the latency period, ii) probability of causation (POC) of a tumor due to radiation, and iii) tumor size.

METHODS

Patients (n = 465) aged up to 50 years at diagnosis who lived in April, 1986 in six northern, most radiocontaminated regions of Ukraine were studied.

RESULTS

Latency period was statistically significantly associated with the reduction of POC level, tumor size and the frequency of fully encapsulated MPTCs. In contrast, the frequency of oncocytic changes and the BRAF^V600E mutation increased. Invasive properties and clinical follow-up results did not depend on latency except for a lower frequency of complete remission after postsurgical radioiodine therapy. The POC level was associated with more frequent extrathyroidal extension, and lymphatic/vascular invasion, less frequent oncocytic changes and BRAF^V600E , and did not associate with any clinical indicator. Tumor size was negatively associated with the latency period and BRAF^V600E , and had a statistically significant effect on invasive properties of MPTCs: both the integrative invasiveness score and its components such as lymphatic/vascular invasion, extrathyroidal extension and lymph node metastases increased. The frequency of total thyroidectomy, neck lymph node dissection and radioiodine therapy also increased with the larger tumor size. The duration of the latency period, POC level or tumor size did not associate with the chance of disease recurrence.

DISCUSSION

In summary, we did not observe overall worsening of the clinicopathological features or treatment results of radiogenic MPTCs that could be associated with the latency period or POC level, suggesting that radiation history did not strongly affect those in the analyzed MPTC patients. However, the increase in the invasive properties with tumor size indicates the need for individual risk stratification for each MPTC patient, regardless of radiation history, for treatment decision-making.

[Probability of Causation (PC): historical motivations and legal transposition]

OBJECTIVES

The Probability of Causation (PC) was introduced to compensate objectively and more possible legally the U.S. diseased subjects involved in the nuclear armament activities.

METHODS

The methodology is related to the attributable risk concept, but it is widely different from it, since it doesn't evaluate the "attributablity" from a collective point of view, but from a "personalistic" point, that is from the particular exposure condition, from the specific physical parameters and from the biological individual features of the single exposed subject. So the PC become an evaluation of the harm probability "tailored" for "that" specific exposed person, on the basis of the epidemiological indications coming from an exposed group with very similar characteristics of the under investigation individual. This is clearly possible owing to the large and exhaustive amount of epidemiological studies in the specific field of radiation exposure. The process to reach the PC adoption took a long time, was plodding and politically thwarted and various reexaminations and bills during time were necessary to extended the laws to the different exposure categories.

RESULTS

Now in the U.S. three departments (Health, Energy and Labour) are involved in the evaluation processes; they gather the personal, dosimetric and clinical data and with a computer program (usable on line also) based on the updated knowledge, evaluate the eligibility for compensation on the basis of the "more likely than not" criterion.

CONCLUSIONS

The method meets the interest and the favor at international level and organizations in prominent positions in the pacific use of nuclear energy and in the radiation protection fields, like: NCRP, IAEA, WHO, ILO,... fight for it use. Now many institutional organism and the more enlightened justice courts utilize the PC to settle cases (increasing in frequency) in work and health activities, for which more often compensation claims are dealing with.

[AIRM recommendations for the application of probability of causation method.]

OBJECTIVES

L'applicazione del metodo della Probability of Causation (PC) è certamente ampio poiché è oggi lo strumento riconosciuto per la individuazione del nesso di causa non solo nelle richieste di indennizzo in ambito assicurativo (per il quale è stata utilizzato inizialmente) ma anche per dirimere contenziosi giuridici in ambito civilistico e penalistico.

METHODS

Thanks to the Italian Association of Medical Radiation Protection (AIRM), PC method has been recently proposed as an aid for the radiation protection occupational physician in medical assessments involving both the mandatory actions that, in case of suspicion of occupational disease, the physician needs to perform (report / complaint / reporting) and the expression of the fitness evaluation in case of return to work after cancer and clinical recovery.

RESULTS

For all these uses PC value, calculated through the method, should be used in a flexible manner, and thus lead to different decisions, "modulated" on the basis of purposes and listed contexts; and this not only within the legal framework, but also in the strictly professional one.

CONCLUSIONS

According to different purposes, different PC values are proposed as a reference for the decisions to be taken.

[Oncological disease: dimensions of the phenomenon and role ionizing radiation]

OBJECTIVES

The continuous scientific advances against neoplastic diseases affecting all areas of oncology biomedical research. Age is an extremely important factor in cancer development, since the incidence of cancer increases significantly with age. Because of aging of the Italian population, although the incidence is kept constant, the number of cancer diagnosis is inevitably going to increase over time only to increasing age.

METHODS

Survival after the diagnosis of cancer is one of the main indicators that allow to evaluate the effectiveness of the health system against the cancer disease. The 5-year survival after diagnosis is a widely used indicator. If we consider the relative survival data after 5 years of diagnosis, for cancer cases diagnosed in subsequent three-year periods, from 1990-1992 to 2005-2007, it shows that the 5-year survival has increased significantly over time for both men and women. Many so-called patients "long-term survivors "are of working age and should return to work. This aims to ensure both the mental and social well-being of the worker, both industrial production. For the oncogenic risk assessment by ionizing radiation, the ICRP Publication 60 has referred to the mortality and cancer data collected from 1950 to 1985 by the RERF, Japan-US bi-national institution with headquarters in Hiroshima that leads the research program called Life Span study (LSS), that is the study of the long-term effects on survivors of the bomb A. For the thyroid, instead, reference is made to the data from medical irradiations, as well as for liver and bone, using in this case adapted data relating to exposure to alpha rays (thorium and radio). The interpretation model is the traditional one: the linear dose-effect assumptions without a threshold even at small doses (LNT theory) when epidemiological data are not more informative for statistical uncertainty, although we resort to radiobiological studies.

RESULTS

In transferring the risk among different populations ICRP in Publication 103 accommodates the idea that for each type of cancer is more suitable, from time to time, the additive or multiplicative model or a combination of the two.

CONCLUSIONS

To study the oncogenic role of occupational exposure to ionizing radiation in the onset of neoplastic disease, the probability of cause (PC), is a "reasonable way to address the problem of evaluation of the likelihood that previous exposure to ionizing radiation (IR) is responsible for an oncogenic event "(Committee on Radiation Protection and Measurements - NCRP - Statement N. 7 of 30/09/92).

Who really gets strep sore throat? Confounding and effect modification of a time-varying exposure on recurrent events

Unmeasured confounding is the fundamental obstacle to drawing causal conclusions about the impact of an intervention from observational data. Typically, covariates are measured to eliminate or ameliorate confounding, but they may be insufficient or unavailable. In the special setting where a transient intervention or exposure varies over time within each individual and confounding is time constant, a different tack is possible. The key idea is to condition on either the overall outcome or the proportion of time in the intervention. These measures can eliminate the unmeasured confounding either by conditioning or by use of a proxy covariate. We evaluate existing methods and develop new models from which causal conclusions can be drawn from such observational data even if no baseline covariates are measured. Our motivation for this work was to determine the causal effect of Streptococcus bacteria in the throat on pharyngitis (sore throat) in Indian schoolchildren. Using our models, we show that existing methods can be badly biased and that sick children who are rarely colonized have a high probability that the Streptococcus bacteria are causing their disease. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.