Aim. To study the ultrastructural features of rectal cancer cells and to detect signs of mitochondrial translocation from the tumor to the resection line area with an assessment of the possibility of the formation of new malignant cells. Materials and methods. The present study encompassed the data obtained from 44 patients with an average age of 66 (58–73) years, who underwent surgical intervention for rectal cancer T2–3N0M0 with differentiation grade G2. A portion of the tumor specimen and intestinal tissue along the resection line were preserved in a formaldehyde-glutaraldehyde fixative solution. Standard methods of section preparation were employed. Sections were subsequently examined using a Jeol JEM-1011 electron microscope (JEOL Inc., Japan).

Results. The ultrastructure of rectal adenocarcinoma was characterized by a high density of arrangement and varying sizes and shapes of tumor cells with a large nucleus and deep invaginations of the nuclear membrane, as well as an accumulation of multiple mitochondria at one of the cell poles. The process of pinching off a cytoplasmic fragment, which was found to be densely packed with mitochondria, was observed. This phenomenon was subsequently identified as a mitochondriome. Following this observation, the mitochondria were found to have translocated into healthy intestinal tissues along the resection line. Electron diffraction data revealed the active movement of mitochondria in the form of small spheroids and mitovesicles along the boundaries of the multilayer structure of the rectal submucosa, and subsequent fusion into large organelles capable of implementing nuclear synthesis from transported mitochondrial and nuclear DNA. We observed the presence of individual nuclear structures in conjunction with groups of mitochondria, followed by the self-assembly of abnormal cells.

Conclusion. The ultrastructural analysis of rectal adenocarcinoma indicates the need for mitochondrial translocation to free up intracellular space and prevent the metabolic threat of reactive oxygen species (ROS) accumulation in tumor cells. It also points to the key role of mitochondria in initiating tumor energy and information transfer as leaders of these processes. This observation suggests the possibility of early recurrence and metastasis in rectal cancer cases.