Cancer and Heredity Is Cancer

Cancer and Heredity

Is cancer inherited? Are you predisposed to cancer if you have a family history of certain type of cancer? These questions have perplexed the medical community and the general public alike. While some maintain that cancer is free of genetic burden, there are others who feel that opposite is true and that genes are responsible to some extent. But in the etiology of cancer multitude of recent researches have been unable to discover one specific cause of cancer. There is no indisputable cause or if there is, it has not been found yet. In researches dating back to 1930s, it was admitted that no single cause of cancer could ever be established. British Medical Journal in 1938 agreed: "The idea has long been abandoned that the "cause of cancer" will be discovered, and it is now recognized that a malignant neoplasm is the resultant of a number of factors and that these factors are themselves variable according to the site and nature of the growth."

What the researches and controlled investigations have shown so far is that certain environmental factors were found in incidences of cancer but whether they alone were responsible for causing the cancer has not yet been determined. For example skin cancer has often been associated with solar radiation but whether several other factors have also been found to affect cancer causation such as ethnicity, pigmentation and family history. Hence while strong association may exist, it certainly doesn't prove causation. The same stands true for the connection between heredity and cancer.

Heredity or genes have shown strong association with development of cancer in many cases but since they appear along with other possible causes, it cannot be said if heredity alone is responsible for certain types of cancer. Hereditary causes are just as much to blame in cases of some cancers as environmental or social factors are in others. For example smokers have often heard that smoking leads to lung cancer. But lung cancer is found just as commonly among non-smokers. But research shows that "among heavy smokers,…, the innate predisposition to bronchogenic carcinoma is, on average, some nine times higher among those who do than do not develop the disease in a lifetime." (Nery, p. 206) Among smokers too, some other genetic or environmental factors may put them under even higher risk.

Thus it can be said that heredity along may not be the cause of any cancer but the causes in all cases may be both environment and genes. Mulvihill (1980) said that "the cause of cancer is unknown and gene frequencies, as well as environment, can differ worldwide" thus confirming that gene and environment are responsible in varying degrees. In some patients, genes may play a major role in predisposing them to cancer while in other it may actually be the environment.

It is however true that recent trends indicate an increased recognition of hereditary in development of cancer. The most important reasons include "spontaneous cancer occurrences i.e. without the mediation of any known or perhaps even any likely extrinsic cause; significant non-random cancer distributions, e.g. among individuals, families, and ethnic groups; and involvement of certain specific normal and developmentally vital inherited genes." (Nery, 207) Certain types of genes have been found to contain a higher risk of cancer such as polyposis or XP. It has been found that people with polyposis trait are likely to develop cancer by the age of 40 and most certainly by the age of 70. This finding has been around for decades even though modern research tends not to blame heredity entirely for development of any type of cancer.

Studies have not been able to develop any significant link with heredity in any type of cancer to the extent that it could solely be held responsible for cancer. However it fully recognizes the role of heredity in predisposition to cancer. It has also been said that some cancers which are found to be more "hereditary" in nature than others like breast cancer, there is a strong tendency to believe that individual's own genome and its reaction to a particular gene determines the risk of developing cancer.

However while no single cause of cancer can be established and it is true that heredity only increases the risk of developing cancer, there are still certain types of cancer where the risk is higher and more pronounced. These types of cancers were first discovered by Henry Lynch in 1960s and he called them "hereditary cancers." He believed that discovery of such cancer was vital to early identification of cancer risk in patients with family history of cancer. The two more prominent types were breast and colon cancer. Even though medical community considers a patients with family history of breast or colon cancer high risk, there is a common tendency to not focus too much on hereditary aspect. While this may have opened new avenues of research, this has also stifled the research in the field of cancer genetics as Lynch felt back in 1960s.

"Henry T. Lynch thought that he had discovered the existence of hereditary cancers among Nebraskan families in the 1960s, his hope was that it would lead to more effective means of cancer control. Lynch argued that the identification of such cancers offered tremendous opportunities for improving detection and treatment. If cancer ran in families, he claimed, the discovery of a hereditary cancer in one family member should be an alert to the possibility of cancer in others, and so prompt careful scrutiny for any signs that might indicate the presence of the disease in "healthy" individuals. However, in the 1960s and 1970s & #8230;cancer experts doubted his claim to have identified hereditary cancers, and ACS education efforts routinely stated that cancer was not a hereditary disease. Thus, Lynch's scheme for improving cancer detection and treatment seemed to falter almost before it began." (Cantor, 2006)

Following Lynch's research however, more people entered the field and began investigating the connection between cancer and heredity. Knudson in his research found that gene mutation plays a key role. He found that while people with positive family history are at a great risk of developing some types of cancers, almost equal number of people with apparent lack of family history of cancer can develop the same type. He consulted many researches and discovered that the reason behind this was bilaterally affected parents. The children of such parents were equally at risk even if there was no family history of cancer. However children of unilaterally affected parents with no family history had a very low risk of developing certain type of cancer. He also then explained how gene mutation differed in hereditary and non-hereditary types of cancer.

Discussing the case of retinoblastoma, Knudson explained that this is one type of cancer which has often been connected with genes. But upon investoigation he discovered that 50% of offspring of affected parents were affected with tyhis cancer. This meant that there was a subgroup that accounted for the other cases of retinoblastoma. And that could also explain why some children will develop cancer and others won't even with affected parents. He thus found that: "the offspring of bilaterally affected survivors with no previous family history of the tumor do have a very nearly 50T probability of being affected, just as with individuals with a positive family history, whereas the offspring of unilaterally affected individuals with a negative family history have only a 10 to 15% risk. Yet when offspring are affected, the fraction with bilateral tumor is high (60 to 70%), whether the parent had unilateral or bilateral disease." (p. 77-78)