[Which samples for molecular biology analyses: Prerequisites and limits]

Molecular analyses performed on cell and tissue samples play a major diagnostic, prognostic, and theragnostic role. Their complexity and diversity, as well as that of the biological matrix involved (formalin-fixed paraffin-embedded tissue, frozen tissue, cytological sample, liquid biopsy), are increasing. The tumor cell content of the sample is an important limiting factor as well as the quality and quantity of nucleic acids extracted from the initial matrix. Therefore, it is crucial to understand and manage the conditions of sample preparation and storage, as those will directly impact the quality of the extracted material and constrain the types of analyses that will be performed. This article highlights the key pre-analytical steps as well as the limitations and interpretative biases that may result from mishandling of the samples.