Cancer cells are characterized by an increased telomerase activity. The enzyme is responsible for reconstruction of
telomeres. Telomeres, as specialized nucleoproteins that are located at the end of chromosomes, provide genome
stability and integrity. The most important consequence of their restore in cancer cells is their immortality. The studies
carried out within last few years on telomerase and telomere length indicate that their regulation is controlled
by factors released during carcinogenesis i.e. hormones and cytokines. Consequently, those factors also modulate
telomerase also in normal cells.
This causes changes in the human organism even at the local area (cancer initiation at a single cell level) which may
be reflected by alterations in whole organism (including leukocytes). The latest studies point to some differences in
the measured telomere length in leukocytes between adenocarcinoma patients and control subjects. Considering
the results of previous studies it seems justified to adopt the thesis that telomere length (or telomerase activity) in
leukocytes can be evaluated as a marker of tumor occurring at a very early stage of carcinogenesis. Thus, it seems
that telomere length measurement in leukocytes, as a low-invasive method, might be a good method for predictive
assessment of carcinogenesis. In this work we focused on potential application of telomere length analysis as a prognostic parameter at the early stage of cancer development in breast and lung cancer. We also report on numerous methods of telomere length analysis showing their strengths and weaknesses.