The cancer stem cell theory elucidates not only the issue of tumour initiation and development, tumour's ability to metastasise and reoccur, but also the ineffectiveness of conventional cancer therapy. This review examines stem cell properties, such as self-renewal, heterogeneity, and resistance to apoptosis. The 'niche' hypothesis is presented, and mechanisms of division, differentiation, self-renewal and signalling pathway regulation are explained. Epigenetic alterations and mutations of genes responsible for signal transmission may promote the formation of cancer stem cells. We also present the history of development of the cancer stem cell theory and discuss the experiments that led to the discovery and confirmation of the existence of cancer stem cells. Potential clinical applications are also considered, including therapeutic models aimed at selective elimination of cancer stem cells or induction of their proper differentiation.

Abstract:Background: Epidemiological data show that colorectal cancer (CRC) is the second most frequent malignancy worldwide. The involvement of "minor impact genes" such as XME and DNA-repair genes in the etiology of sporadic cancer has been postulated by other authors.Aim: we focused on analyzing polymorphisms in DNA-repair genes in CRC. We considered the following genes involved in DNA-repair pathways: base excision repair (OGG1 Ser326Cys, XRCC1 Trp194Arg and Arg399Gln); nucleotide excision repair [XPA (-4)G/A, XPC C/A (i11) and A33512C (Lys939Gln), XPD Asp312Asn and A18911CMaterial and methods: The study group consisted of 133 patients diagnosed with sporadic CRC, while the control group was composed of 100 age-matched non-cancer volunteers. Genotyping was performed by PCR and PCR-RFLP. Fisher's exact test with a Bonferroni correction for multiple testing was used.Results: We found that: i) XPC C/A (i11) heterozygous variant is associated with increased risk of CRC [OR is 2.07 (95% CI 1.1391,3.7782) p=0.038], ii) XPD A18911C (Lys751Gln) is associated with decreased risk of CRC [OR=0.4497, (95% CI 0.2215,0,9131) p=0.031] for an individual with at least one A allele at this locus. Conclusions:1. the XPC C/A (i11) genotype is associated with an increased risk of sporadic colorectal cancer.2. the NER pathway has been highlighted in our study, as a most important in modulation of individual susceptibility to sCRC.

Despite great progress in research on the subject, the involvement of autophagy in colorectal cancer (CRC) pathogenesis (initiation, progression, metastasis) remains obscure and controversial. Autophagy is a catabolic process, fundamental to cell viability and connected with degradation/recycling of proteins and organelles. In this study, we aimed at investigating the relative expression level of mRNA via Real-Time PCR of 16 chosen genes belonging to Atg8 mammalian orthologs and their conjugation system, comprising GABARAP, GABARAPL1, GABARAPL2, MAP1LC3A, MAP1LC3B, MAP1LC3C, ATG3, ATG7, ATG10, ATG4A, ATG4B, ATG4C, ATG4D, and three genes encoding proteins building the multimeric ATG16L1 complex, namely ATG5, ATG12, and ATG16L1, in 73 colorectal tumors and paired adjacent normal colon mucosa. Our study demonstrated the relative downregulation of all examined genes in CRC tissues in comparison to adjacent noncancerous mucosa, with the highest rate of expression in both tumor and non-tumor tissues observed for GAPARBPL2 and the lowest for MAP1LC3C. Moreover, in patients with advanced-stage tumors and high values of regional lymph nodes, statistically significant downregulation of ATG4D expression in adjacent normal cells was observed. Our study confirms the role of autophagy genes as cancer suppressors in colorectal carcinogenesis. Furthermore, in regard to the ATG4D gene, we observed the influence of tumor microenvironments on gene expression in adjacent colon mucosa.