BACKGROUND INFORMATION: Mitosis is crucial for the faithful transmission of genetic material, and disruptions can result in chromosomal instability (CIN), a hallmark of cancer. CIN is a known driver of tumor heterogeneity and anti-cancer drug resistance, thus highlighting the need to assess CIN levels in cancer cells to design effective targeted therapy. While micronuclei are widely recognized as CIN markers, we have recently identified the toroidal nucleus, a novel ring-shaped nuclear phenotype arising as well from chromosome mis-segregation. RESULTS: Here, we examined whether increasing nuclear envelope stiffness through lamin A/C overexpression could affect the formation of toroidal nuclei and micronuclei. Interestingly, lamin A/C overexpression led to an increase in toroidal nuclei while reducing micronuclei prevalence. We demonstrated that chromatin compaction and nuclear stiffness drive the formation of toroidal nuclei. Furthermore, inhibition of autophagy and lysosomal function elevated the frequency of toroidal nuclei without affecting the number of micronuclei in the whole cell population. We demonstrated that this divergence between the two CIN biomarkers is independent of defects in lamin A processing. CONCLUSIONS AND SIGNIFICANCE: These findings uncover a complex interplay between nuclear architecture and levels of CIN, advancing our understanding of the mechanisms supporting genomic stability and further contributing to cancer biology.