“Technical but fundamental errors” lead to retraction of brain tumor paper

The journal Neuro-Oncology has retracted a 2011 paper by a group of researchers in Japan who had purported to find a genetic mechanism for how fluorescence can be used to diagnose certain brain tumors.

The paper, “Enhanced expression of coproporphyrinogen oxidase in malignant brain tumors: CPOX expression and 5-ALA–induced fluorescence,” reported measurements using quantitative real-time (qRT)-PCR.

As the retraction notice explains:

Neuro-oncology regrets to inform readers that this article has been retracted at the authors’ request.

The authors have recently identified technical but fundamental errors in the preparation of the standard curve of quantitative real time PCR (qRT-PCR).

As the consequence, the experimental results presented in the paper are wrong with respect to mRNA expression levels, in particular those presented in Figures 3 and 4. The authors have investigated the technical mistake by examining all the data recorded in laboratory books and a laboratory computer as well as by newly performing western blot analysis for the CPOX protein in surgically resected samples from malignant glioma patients. The subsequent investigation shows that CPOX expression level is not a key factor for 5-ALA-induced fluorescence in malignant brain tumors. The authors sincerely apologize for the technical mistakes made in their study.

Here’s the abstract of the article:

In photodynamic diagnosis, 5-aminolevulinic acid (5-ALA) is widely used for the fluorescence-guided resection of malignant brain tumors, where 5-ALA is converted to protoporphyrin IX, which exhibits strong fluorescence. Little is known, however, about the detailed molecular mechanisms underlying 5-ALA–induced fluorescence. To resolve this issue, we analyzed transcriptome profiles for the genes encoding enzymes, transporters, and a transcription factor involved in the porphyrin-biosynthesis pathway. By quantitative real-time (qRT)-PCR, we measured the mRNA levels of those genes in a total of 20 tumor samples that had been surgically resected from brain tumor patients at the Department of Neurosurgery of Osaka Medical College from 2008 to 2009. We selected 10 tumor samples with no 5-ALA–induced fluorescence, among which 2 were glioblastomas and 8 were metastatic brain tumors. Another 10 tumor samples were selected with strong fluorescence, among which 7 were glioblastomas and 3 were metastatic brain tumors. The qRT-PCR analysis study of these latter 10 samples revealed predominantly high levels of the mRNA of the coproporphyrinogen oxidase (CPOX) gene. The high mRNA level of CPOX expression was significantly well correlated with the phenotype of strong 5-ALA–induced fluorescence (P = .0003). These findings were further confirmed by immunohistochemical studies with a CPOX-specific antibody. It is concluded that induction of CPOX gene expression is one of the key molecular mechanisms underlying the 5-ALA–induced fluorescence of malignant brain tumors. The induction mechanism for the CPOX gene in brain tumors remains to be elucidated.

The paper has been cited twice, according to Thomson Scientific’s Web of Knowledge.