Molecular changes characteristic of malignant tumors such as genetic mutations or altered levels of specific transcripts
and proteins are sometimes observed within the morphologically and histologically normal tissue adjacent to the
tumor. Such an area of morphologically normal yet molecularly changed tissue is called a molecular margin of tumor.
It has been suggested that molecular changes observed in this area might be followed by a further transformation
into a malignant tumor. The efficacy of surgical treatment of the tumor depends on complete resection of cancer
cells, hence local recurrence and failure of the treatment might result from tumor cells residing outside the resected
area. However, a local recurrence could also result from malignant transformation of cells in morphologically and
histologically normal tissue adjacent to the tumor where molecular cancer-initiating changes were pre-existing. Hence
identification and delineation of molecular margins of tumor (and removing them together with the cancer) might
be crucial for the efficacy of the treatment. There are several diagnostic tools that can be used for identification and
characterization of tumor molecular margins. The most commonly used include immunohistochemistry and PCR-based
methods, which allows analysis of pre-selected proteins, transcripts and genes. Most recently, technically advanced
methods of genomics and proteomics have been also proposed in studies of molecular margins of cancer, including
molecular imaging of tissue by mass spectrometry (so called Imaging Mass Spectrometry).