The copious publications of high-profile German cardiologist Bodo-Eckehard Strauer — who has long claimed that stem cells derived from bone-marrow cells can repair damage in diseased hearts — have come under new attack.

Strauer, who retired from the University of Düsseldorf in 2009, has been a controversial figure in Germany since he first claimed clinical success with the approach in 2001. Many stem-cell scientists have been openly sceptical of his claims, which have been reported enthusiastically in the media.

An article published this week in the International Journal of Cardiology dissects 48 of the papers from his group and exposes a series of problems, including arithmetic errors in the presentation of statistics and identical results in papers presenting different numbers of patients. The authors also searched systematically in all of the papers for discrepant information — pairs of statements that could not both be true.

They document hundreds of errors. For example, in some papers patient groups are said to be randomized, whereas in others patients with identical outcomes are reported as being non-randomized to treatment and control groups. “And when we ran the statistical tests on the control groups, we found many amazing P values of up to 10–60 and 10–108,” Darrel Francis, a cardiologist at Imperial College London and one of the study’s co-authors, told Nature.

In a press release, Francis says:

Looking deeper, the seemingly comprehensive and decisive proof of efficacy gradually unravelled … the more we thought about it, the less we could understand. In the end we couldn’t even work out whether some of these studies were randomised or not, or how many patients had really been studied. This is an unusual situation for studies which report being able to make the difference between life and death.

In response to a request for comment on the allegations, Ruben Engel, Strauer’s lawyer, wrote in an e-mail to Nature:

In manuscripts of the working group of our client have appeared, unfortunately, arithmetic errors, what can never be excluded completely. Our client apologizes for this to the publishers resp. has already corrected these errors [sic]. In one case, one picture in a publication — of approx. 20 (!) pictures in the whole study — was mistaken. This picture showed one of a huge number of parameters of the documented investigation results. No advantage of the published results was reached by the use of the picture: Even if the picture had been left out, the statement of the study would remain completely unchanged.

The University of Düsseldorf began an investigation into some of Strauer’s published papers last December.