Question

2c. Explain two types of tumor dormancy which result in the development of primary cancer in individuals without history of cancer, and tumor relapse in cancer survivors.

Answer 1

Recurrence of cancer after several years even of surgical removal of tumors led to the origination of concept of tumor dormancy.

Tumor dormancy is defined as arrest of tumor cell growth either in primary or metastatic state.

Tumor mass is a dynamic structure which maintains an equal number of cells by maintaining an equilibrium between cell proliferation and cell death. Tumor mass dormancy includes two models:

1. Angiogenic dormancy : Formation of new blood vessels (angiogenesis) is regulated by pro angiogenic and anti angiogenic factors in order to form intense network of blood vessels in the growing tumor mass which is required for meeting increased energy requirements of the cell. When equilibrium shifts towards pro angiogenic factors, it results in tumor progression. Before this process there is cell death due to lack of oxygen and nutrients in the regions which are located distantly from newly forming blood vessels, this state of equilibrium between proliferation and death of cancer cells known as angiogenic dormancy.

2. Immune mediated dormancy : Immune system plays vital roles in inhibition of tumor establishment and in tumor mass dormancy. T cells( CD 8+) play major roles in tumor dormancy at metastatic sites. Single nucleotide polymorphisms are reported in the cells of primary tumors and those of metastatic sites, which helped the circulating tumor cells to escape immune surveillance.