Deletions and rearrangements of the short arms of chromosome 12 are frequent chromosomal changes in patients with haematological malignancies. The loss of genetic material in tumour cells is usually indicative of the inactivation of genes with tumour suppressor function. The region of 12p has been largely studied by molecular genetic and molecular cytogenetic methods to identify the tumour suppressor genes included in leukemogenesis. The gene TEL/ETV6 is not classical tumour suppressor gene but it is often deleted or rearranged in variety of hematological malignancies. In this study we present a group of 10 patients with deletion del(12)(p) found by conventional cytogenetic analyses. Patient´s diagnoses were either lymphoid or myeloid leukaemias. We applied molecular-cytogenetic methods (fluorescence in situ hybridization- FISH) with locus-specific probe LSI TEL/AML1 to assess deletion of TEL/ETV6 gene on 12p.To exclude translocations of 12pweuse FISH with whole chromosome painting probe for chromosome 12 and mFISH in patients with complex karyotype. Deletion of TEL/ETV6 was found in five of eight examined patients. No translocations of 12p were confirmed. The region closely linked to this gene probably contains one or more genes (tumour suppressors) which play the role in progression of oncogenesis. We suppose that in patients with unconfirmed deletion of TEL/ETV6 other genes with tumour suppressor function were inactivated.

        Key words: Deletion del(12)(p), TEL/ETV6, leukaemias