Cancer dormancy

Dormancy is a stage in cancer progression where the cells cease dividing but survive in a quiescent state while waiting for appropriate environmental conditions to begin proliferation again. Quiescence is the state where cells are not dividing but at arrest in the cell cycle in G0-G1. Dormant cancer cells are thought to be present in early tumor progression, in micrometastases, or left behind in minimal residual disease (MRD) after what was thought to be a successful treatment of the primary tumor.

Cancer dormancy is not yet fully understood, but some researchers have performed mathematical modeling to explain the occurrence of cancer dormancy as a characteristic of all migrating tumor cells as part of an evolutionary process of selection and mutation. Recently, scientists from Aga Khan University Pakistan, have extended the studies of encystation in Acanthamoeba to induce dormancy in Prostate cancer cells lines and understanding of the signalling pathways that are involved. This eukaryotic encystation in Acanthamoeba spp., is known to involve a crosstalk between the trophozoite form of the cell and unfavourable microenvoirment that induces it. It is thought that once tumor cells disseminate and begin to migrate to a new site to metastasize, the interaction of the tumor cells with that microenvironment determines whether the cells will proliferate and form metastases or undergo growth arrest and enter cancer dormancy. It is suggested that the disseminated cells choose dormancy when the new environment is not permissive in situations such as cellular stress or a lack of available growth factors. These dormant cells can stay in this state for long periods of time and can be clinically undetectable. However, these cells can be dangerous because they can strike back years after the doctor and patient believe the patient is cured. They can exist in a quiescent state for many years, but the dormancy period can be interrupted to start proliferating uncontrollably and form metastases that cannot be treated. Cancer dormancy is often associated with minimal residual disease (MRD) where some tumor cells are left behind after a treatment and can persist either at the primary tumor site or as disseminated cells that are proliferating or dormant. MRD has been found in a widespread range of cancers including but not limited to: breast, prostate, colon, gastric, colon, pancreatic, head and neck, neuroblastoma, leukemia, melanoma, and others. These cells are often found in the bone marrow, but are also found in other organs and usually indicate poor prognosis for the patient.

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