10% of all cancers are hereditary.In other words, it means that mutations (variations) in certain genes specific to that organ pass from one generation to another.

If a person carries one of the abnormal genes, they are much more likely to get cancer at some stage in their life than normal people, and they can pass on the same risk to their own children. Type ofcancers in which family history is important are breast cancer, colon cancer, ovarian cancer, prostate cancer, melanoma and endocrine cancers.If your second- or third-degree relatives have one or more of these cancers it is recommended to talk to your doctor.

Basic Concepts in Cancer Genetics

  1. “Germline” mutation: mutations that occur in germ cells (gamet, sperm or ovum) in the gonads.People with this type of mutation can pass it on to their children.The child who inherited the mutation will carry that mutation not only in germ cells, but in all cells of his body.Germline mutations are responsible for hereditary cancers.
  2. Somatic mutation: mutations that occur in body cells other than germ cells, namely somatic cells. Such mutations do not pass on to the next generation, their biological consequences only affect the individual that has it. Somatic mutations play a role in the development of non-hereditary cancers, that is, sporadic cancers.
  3. Proto-oncogene: genes that play a driving role in cell proliferation. Cell proliferation is normally carried out according to physiological requirements and in a controlled manner. The main functions of protooncogenes are shown below:
    • transcription factors
    • growth factor and growth factor receptors
    • suppression of apoptosis
    • modification of chromatin
    • intracellular signal transmission
    • membrane-associated G proteins
  4. Tumor suppressor genes: genes that play a negative role in cell proliferation. Tumor suppressor genes that directly suppress proliferation are called “gatekeeper” genes.


Cancer is a clonal disease that develops as a result of changes made by various factors in micro and macro environment on genetic material and the development process has multiple stages.In some cancers, genetic factors cause these multiple stages process to start easily. In this case, it is mentioned that there is a “genetic predisposition” for cancer.Thanks to advances in molecular genetics, different genes that lead to the predisposition to cancer have been identified. Families / individuals with mutations of these genes are known to have a high risk of cancer.The hereditary form of cancer is characterized by early age of diagnosis, high penetration, bilateral appearance in paired organs, inheritance from both parents, and coexistence with other types of tumors.If the same type of cancer is observed in the family it is defined as hereditary cancer, and if different types of cancers are observed it is defined as the cancer family.  The presence of the following cases in the family should be considered as important cancer predisposition.

  • Cancer cases in >2generations
  • Having 2 or more cancerous individuals in a generation
  • Individuals diagnosed at the age below average
  • Having an individual with more than one cancer
  • The presence of cancers in the individual with some syndromes
  • Breast and ovary
  • Colon and uterus
  • Breast and thyroid
  • Melanoma and pancreas
  • Sarcoma and leukemia

The genes responsible for the development of cancer predisposition are tumor suppressor genes. Tumor Suppressor Genes (TSG) encode proteins that control cell cycle or provide DNA repair. They are responsible for maintaining the integrity and sustainability of the genome with these functions. They are divided into two main groups: Gate-keepers and Care-takers. The Loss of Heterozygosity (LOH) in these genes causes accumulation of mutations in the cell.

The cases when cancer genetic counseling is beneficial are the following:

  • People with the same type of cancer or interrelated cancer (breast / ovaries / pancreas, colon / uterus) in more than one relative on the same side of the family
  • People with diagnosed cancer at an early age (breast cancer < 45 years, colon cancer < 50 years)
  • People with multiple cancers (breast / ovaries; colon / uterus)
  • People with rare cancers (such as male breast cancer, Medullary thyroid cancer)