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Avatar #681861
am Dienstag, 8. Oktober 2019 um 21:50

" There is no message to the public here – I suspect these results are just noise.” Indeed, there is

Kommentar zur Nachricht
E-Zigaretten mit Nikotin erzeugen bei Mäusen Lungenkrebs und Urothelhyperplasien
vom Dienstag, 8. Oktober 2019
Prof John Britton, Director of the UK Centre for Tobacco & Alcohol Studies and Consultant in Respiratory Medicine, University of Nottingham, said:

“This study explores the effect of exposure to nicotine ecig vapour on mice. It shows that exposure to ecig vapour with nicotine causes more cancers than fresh air, but no more than you might reasonably expect by chance.

“It also shows that e-cig vapour without nicotine causes fewer cancers than fresh air.

“The findings are based on very small numbers and need to be interpreted with extreme caution.

“The comparison between mice breathing vapour and mice breathing air is not statistically significant. There is no sample size justification and no power calculation. There is no message to the public here – I suspect these results are just noise.”

Prof Peter Hajek, Director of the Tobacco Dependence Research Unit, Queen Mary University of London (QMUL), said:

“The study has unclear relevance for human vapers.

“Rodents were exposed to what are for them huge concentrations of chemicals that bear no resemblance to human exposure from vaping. Several animals in fact died during these exposures.

“The authors assigned the effects they observed to a carcinogen NNK – but NNK has been measured before in human vapers, and it is known that exposure from vaping is either negligible or none.”

‘Electronic-cigarette smoke induces lung adenocarcinoma and bladder urothelial hyperplasia in mice’ by v et al. was published in PNAS at 8pm UK time on Monday 7 October.

DOI: 10.1073/pnas.1911321116
Avatar #781928
am Mittwoch, 9. Oktober 2019 um 23:08

Study’s main claims – and are they supported by the data (?)

The study’s main claim is that electronic cigarette (ecig) vapour causes lung adenocarcinoma (lung cancer) and bladder urothelial hyperplasia (an increased number of cells lining the bladder) in mice.

This is somewhat supported by the data in the study, though there are a number of serious limitations in the study which may have caused considerable bias, therefore affecting the validity of the data and subsequently this claim.

It would be wrong to conclude from this study that vaping is carcinogenic in humans. Notably, the authors do not state that their study is conclusive – only that it warrants further research, which is a balanced conclusion to make and is something it would be difficult to disagree with.



The study is a randomised trial and so therefore has the potential to demonstrate a causal relationship in mice; however, there are a number of limitations which could have biased the study’s results (see below).
The authors have used ecig juice and aerosol generators that are typically available commercially.
Although there is a huge amount of uncertainty in the results, there is the potential for a fairly large increased risk in adenocarcinoma in mice exposed to ecig vapour.

Limitations of the study

Was this a proper blind trial? It is not clear whether the group allocation was kept secret from either the researchers administering the compounds or those assessing the histopathology. This is known to potentially lead to very biased results.
The statistical evidence of an effect on lung carcinoma is very weak
The authors perform multiple statistical tests which increases the probability of a chance positive finding
The choice of the statistical test is not appropriate for this type of data. Generally the stats in this paper are very poor.
The authors do not provide indicators of uncertainty (such as confidence intervals) for all the comparisons, which makes impossible to assess the precision of the results.
The study has a small sample size and they have not performed a power analysis (see glossary)
The authors say animals were randomly allocated to different groups, but the numbers in each group (45, 20, 20) are perfectly rounded, which would be very unlikely to occur by chance without using a more technical method or randomisation. This may suggest the authors have not used a truly random technique for allocation, which is known to introduce a lot of bias. Moreover, mice dying before the end of the study were excluded from the analysis, which may also cause bias.

A final point is that this study is in mice, not in humans, and mice may respond to nicotine or ecig vapour differently for a number of reasons.

It is also unclear if the exposure on the mice is typical of exposure in humans.

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