MALDI imaging mass spectrometry in cancer research: combining proteomic profiling and histological evaluation.

Despite the tendency to regard tumors as a simple mass of cancer cells, tumors have a high degree of complexity that is difficult to access with most analytical methods. Because the cancer tissue itself directly contains all information concerning proteomic and genetic changes, it represents the best possible sample material for any molecular research. However, an analytical method should also take advantage of morphological information contained within the cancer tissues, a feat that is not easily possible with methods based on sample homogenization such as conventional mass spectrometry. Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry represents a method that allows the combination of mass spectrometric analyses with simultaneous histological evaluation to analyze various analytes such as proteins, peptides, lipids, or exogenous and endogenous small molecules. Spatially resolved mass spectrometric measurements are directly taken from a tissue section without destroying it. This combination allows for direct analysis of tumor samples while retaining the morphological information contained within the tissues, making it a very valuable tool in cancer research by complementing other currently used approaches. In this review, we discuss the position that MALDI imaging mass spectrometry currently occupies in the field of cancer research by showing its fields of application as well as the results and new discoveries that could be obtained using this method.