The method of choice used for preparing tissue samples can lead to biased results in the analysis of cancer patient survival. For microscopic analysis, full tissue samples provide a better picture of the immune cell activity in a tumor compared to tissue-sparing punch biopsies.
These were the findings of a Medical University of Vienna study of the immunohistochemistry of tumor tissue in rectal cancer patients. The researchers found that when using a punch biopsy, the density of immune cells in the tumor can be underestimated, which might result in a biased survival prognosis.
Lukas Kenner, MD, Medical University of Vienna.
In order to perform a microscopic analysis of a tissue sample, a paraffin section must be prepared. For this, the tissue sample is preserved and subsequently dehydrated and embedded in paraffin blocks. Further on, thin tissue sections of the samples are produced and applied to glass slides. Regularly, a tissue section of the whole surgical specimen of each patient is applied to one slide, so that the full extent of the tumor section is available for analysis.
For quick and efficient microscopic analysis of tumors of multiple patients, small punches of paraffin tumor tissue are compiled onto one slide. This so-called tissue microarray is a tissue-sparing procedure that minimizes the costs of expensive immunohistochemical analyses. Both methods allow the staining of specific protein molecules in the tumor. Digital scanning of the tissue slides allows researchers to quantify the stained protein molecules and assign them to specific tumor compartments by the use of a special software.
As part of the immunohistochemical study, Elisabeth S. Gruber, MD, a specialist in general and visceral surgery at the Medical University of Vienna, and Lukas Kenner, MD, head of the university’s department of experimental pathology and laboratory animal pathology, examined the number of T cells in tissue samples of 75 patients operated on for rectal cancer. One cohort of patients received radiotherapy before the surgery; the other did not. The initial study hypothesis was that radiotherapy modulates tumor immune cell infiltration. In rectal cancer, the density of T cells present in the tumor is crucial for the patient’s survival. Here, analysis was done using software developed in collaboration with the Viennese company TissueGnostics that allows analysis of virtually established tissue microarrays.
By comparing the two methods, the study authors demonstrated that the distribution of T cells in tumor tissue is heterogeneous and thus might be underestimated when using small tissue samples. For the prognosis of rectal cancer survival, the researchers conclude that the assessment of tumoral immune cell density is best and most reliably performed on the basis of a certain minimum area of tumor tissue.
Reference
1. Gruber ES, Oberhuber G, Pils D, et al. The determination of immunomodulation and its impact on survival of rectal cancer patients depends on the area comprising a tissue microarray. Cancers (Basel). 2020;12(3):E563; doi:10.3390/cancers12030563.
