The authors analyzed 66 cases of malignant smooth muscle tumors of the corpus uteri to study different histological types of leiomyosarcoma (LMS). They identified cases of LMS, the phenotype of which was noted to have structures containing a large number of multinucleated cells (at least 10% of the total tumor mass). The incidence of this form of sarcoma was 19.7%. The authors established that these types of LMS were significantly different from its others in molecular biological characteristics; vascular angiogenic and architectonic features; high Ki-67, BrdU-label, and p53 expressions; argyrophilic protein amplification in the nucleolar organizer region; high morpho-densitometric parameters; metabolic activity with respiratory ensemble inversion; high activity of the topoisomerase IIα enzyme of gyrase; more commonly negative receptor status and frequent nuclear translocation of molecular HSP70 chaperone; and an extremely poor outcome.