Les conséquences moléculaires de la fixation et de l’inclusion: exemple des acides nucléiques et des protéines

[Role of the surgical pathology laboratory in the pre-analytical approach of molecular biology techniques]

The advent of the targeted cancer therapies administered to patients, according to the results of molecular biology techniques (in particular, in situ hybridization, "polymerase chain reaction" amplification and sequencing), has modified the practice of the surgical pathology laboratories. The necessity to answer to the needs of physicians for optimizing the medical care for patients who develop cancer has led to a policy of national debate, spurred by the National Institute of Cancer (INCa), in order to implement new procedures in the pathology laboratories. Thus, in addition to the structuring of molecular biology platforms and their labeling by INCa, the upstream control of the steps present between resection of tumor samples and molecular analysis has proved to be crucial. Indeed, the quality of this upstream time, called "pre-analytical" phase, determines the reliability of the molecular biology results and therefore the therapeutic strategy. We describe here the main steps to be checked in the pre-analytical phase. The optimization of this pre-analytical phase within the surgical pathology laboratory aims to reduce or render insignificant the risk of errors of molecular biology tests. These errors can indeed lead to false negative or false positive results whose therapeutic consequences can be particularly harmful to patients with cancer.

MALDI direct analysis and imaging of frozen versus FFPE tissues: what strategy for which sample?

Significant advances have been made in the past decade in the field of mass spectrometry imaging with MALDI ion sources (MALDI-MSI). While MALDI-MSI has high potential in the field of biology and in the clinic, a challenge for MALDI-MSI has been to adapt itself to a greater range of sample types. In particular, much of the biological archived materials for pathology studies are tissue biopsies fixed with paraformaldehyde and embedded in paraffin (FFPE tissues) because of the high stability of such samples. Thus, there has been a need to develop strategies for analyzing FFPE samples as this would allow retrospective studies of past clinical cases on large cohorts of existing samples. Obviously, PAF fixation, by inducing protein cross-linking, causes problems for molecular analysis by MS. We developed on tissue digestion strategies for overcoming these difficulties and allowing molecular data to be retrieved from FFPE samples no matter how long they have been stored. These digestion strategies preserve localization from digested proteins making MALDI-MSI of proteins possible by monitoring the resulting peptides. We present methods and protocols for FFPE samples. These strategies have proven to be valuable for all tested FFPE samples and have opened archived tissues from hospital banks to MALDI-MSI.