Anil Potti and his former Duke colleagues have retracted a sixth paper, this one in PLoS ONE.

According to the retraction notice for “An Integrated Approach to the Prediction of Chemotherapeutic Response in Patients with Breast Cancer,” the withdrawal was prompted by the retraction of a Nature Medicine paper that formed the basis of the PLoS ONE study’s approach:

The chemotherapy sensitivity predictions as reported in this PLoS One article were based on an approach as described by Potti et al. in Nature Medicine (1). Reexamination of the validation datasets used for the Nature Medicine study has revealed the presence of errors in the labeling of clinical response in some datasets (2). Re-analysis of the predictive accuracy with correctly labeled data has shown that in two instances the reported signatures do not predict the response of the validation samples to chemotherapy (2). The authors of the Nature Medicine paper have therefore decided to retract that paper (2). Since the PLoS One article is based on the approach reported in the Nature Medicine article, we have decided to retract the PLoS One article. We apologize to readers for any inconvenience caused by the publication of our article in PLoS One.

The PLoS ONE paper has been cited 29 times, according to Thomson Scientific’s Web of Knowledge. As we reported in January when the Nature Medicine paper was retracted, that paper was cited more than 250 times.

The PLoS ONE retraction means we are likely halfway through all of the paper withdrawals, according to a report in The Cancer Letter of an August 22, 2011 Institute of Medicine meeting:

Robert Califf, director of the Duke Translational Medicine Institute and vice chancellor for clinical research, said that the university has nearly completed an internal investigation of Potti’s published research. “There were about 40 [manuscripts] that had original data that were generated at Duke,” Califf said. “We had an institutional need to understand the veracity of the manuscripts that had the institution’s name on it.” “About a third of the manuscripts are being fully retracted,” Califf said. “About a third are having a portion retracted with other components remaining intact, and about a third seem to be ok.” “In those retractions and partial retractions, there is a clear correlation between the need to withdraw the data and the extent to which the data originated from Dr. Potti,” Califf said. “It looks like they’re fundamentally not reproducible.” No timeframe was given for these retractions.

There’s plenty more in The Cancer Letter’s current issue, including details on the lawsuits filed against Duke, Potti, and his colleagues by a number of former clinical trial participants. The Economist also covers the Potti story this week, and Darrel Ince has a piece on it in the journal Significance.

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