Premature chromosome condensation (PCC) was studied in direct preparations of tissues from patients with haematological diseases and carcinomas of various histological types. PCC was found in 6 out of 166 malignancies (128 haematological cases, 35 carcinomas and 3 malignant effusions) analysed with the GTG-technique. Chromosome analysis revealed S-phase and G1-phase PCC in each case; the frequency of PCC varied between 1, 4 and 8.6% of the metaphases analysed. It is suggested that PCC chromosomes, which represent cell fusion in vivo, are not very rare in naturally-occurring human malignancies, and that cell fusion may affect the malignant phenotype. In conjunction with other factors they may also explain the heterogeneity of tumour cell populations.
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