The researcher Gabriela Debesa, member of the research group at Simbiosis led by Andrés Moya at the Foundation for the Promotion of Health and Biomedical Research of Valencia Region (Fisabio), studied the relationship of the intestinal microbiota with colon cancer in patients with Lynch Syndrome (a hereditary illness that predisposes the development of cancer) using tissue samples in formalin and conserved in paraffin.
The main objective was to figure out if it is possible to obtain information of the microbiome based on samples conserved in this way. This was studied in samples of patients with Lynch syndrome that had developed colon cancer and it was compared if there were differences between the bacterial DNA sequences of the intestinal mucous as well as those of the tumors.
According to Gabriela Debesa, first signatory, who has received a pre-doctoral grant from the Spanish Association Against Cancer (AECC) in Valencia, "It was shown that in the tumoral tissues, there is a greater presence of some bacterial groups associated with tumors in comparison with the normal mucous, such as Fusobacterium nucleatum, Bacteroides fragilis and Campylobacter."
These results had already been obtained previously in samples of fresh tissues, but the new feature of this study has been that it extracts this information from old tissues preserved in formalin and paraffin that were stored in the IBSP-CV, the Biobank for the Biomedical Research and Public Health in the Comunitat Valenciana, which form part of the Valencian Biobanking Network.
In this type of studies, the samples that are normally used are from fresh or frozen tissues, which requires providing samples immediately or depend on complex freezing infrastructures. However, this study has been able to corroborate previous studies, analyzing non-fresh tissue blocks.
Andrés Moya, project's principal researcher, explained that "It is an important development because there is an enormous number of samples preserved, and thus available in the hospitals and biobanks. Classically, samples are taken after surgery from the removed area to be conserved in paraffin blocks. The advantage of this means of preservation is that it does not require special storage conditions and they last for many years."
However, this type of conservation of samples presents some complications. In studying cancer, genomic information is increasingly gaining importance. This method is not as effective in obtaining this information, given that it damages both the human DNA and the bacterial DNA, which is what is used to analyze the microbiome.
Despite these difficulties, we obtained results based on the previous studies carried out with fresh tissue, where the DNA is in optimal conditions for its sequencing."
Vicente Pérez-Brocal, researcher and first signatory of the study
This method offers new possibilities given that it does not limit the samples to fresh tissues available, but many more stored samples can be used. The main application will be being able to carry out a retrospective analysis of the microbiome in our samples preserved in paraffin, as an alternative when fresh tissue is not available for colorectal cancer and other pathologies.
Doctor Antonio Llombart, principal researcher of the Clinical and Molecular Oncology group of Fisabio and president of the Technical Committee of Valencia AECC explained that "This study is a very important step to facilitate the research of how the intestinal microbiota affect the development of colon cancer in people with Lynch Syndrome. This will allow having information to be able to develop new, more effective methods of early diagnosis and prevention, something that is essential in treating this type of cancer, which is very common."
In addition, Doctor Llombart, head of the Service of Medical Oncology at the Hospital Arnau de Vilanova, added that "It is important to keep advancing in the fight against colorectal cancer, which every year affects over 38,790 new patients in Spain and causes the death of over 15,770 people."
For the study, 98 samples were used (one from tumor tissues and one from the healthy mucous for each person) from patients diagnosed with Lynch Syndrome, who were surgically treated between 1996 and 2017. The samples belonged to 21 women and 28 men with an age range of 33 to 87 years.