Fig. 2. Chromosomal instability and cancer invasion.

Chromosomal instability (CIN) is one of the cancer hallmarks and plays an important role in tumour cell migration and invasion. CIN can be represented by gain or loss of whole chromosomes (numerical CIN) and chromosomal rearrangements (structural CIN). Loss of heterozygosity (LOH) that can be attributed to numerical and structural CIN simultaneously, depending on the type of genomic changes resulting in the allele loss, affects the invasive potential of tumour cells. Polyploidy defined as the presence of additional sets of chromosomes drastically changes the genetic landscape of tumour cells, endowing them with high invasive potential. Polyploid giant cancer cells (PGCCs) are found in various cancers and show extreme tumorigenic, invasive and metastatic potential. Aneuploidy when chromosomes can be lost (monosomy) or gained (trisomy) can have different effects on tumour cell invasion: from attenuation of migratory behaviour to its enhancement. Different gene fusions arising from various chromosomal rearrangements affect tumour cell motility through diverse signalling pathways and mechanisms. Amplification defined as a copy number increase of a certain region of the genome leads to enhanced gene expression and, if a gene positively regulates cellular motility, it can accelerate cancer invasion.