My wife and I are both sterile. Is there any danger of passing this on to our children?
Letter to government agency. Juliet Lowell, "Dear Sir"
We inherit a lot of characteristics from our parents that we pretty well take for granted. We inherit arms, legs, livers, and so on. Everything that we are is in some way influenced by our heredity. If an individual inherits a gene that causes death before the age of five, we might say that this may be a cancer-preventing gene. We may also inherit genes that contribute to longevity, which might be considered as pro-cancer-and-heart-disease genes, since cancer and heart disease are primarily diseases of old age. The answer to the question about whether susceptibility to cancer is influenced by heredity is clearly a "yes."
But this is not really the question that most people are deeply concerned about. The question asked is, "My mother died of breast cancer; what are the chances of my doing the same?"
What do we mean when we say that someone whose parents had a particular form of disease has twice the chance of developing the disease? Does it take into consideration whether this difference is due to something genetic, a virus, or some common environmental factor? How much, if any, of these constitutional risks represent heredity and how much they represent other factors is not known? There is, for example, a slight increase in the risk of developing lung cancer in the relatives of people who have had lung cancer, as compared to the controls. This difference is very small when it is compared with the difference between smokers and nonsmokers with regard to the same disease. There is a cultural tendency for the children of smokers to also smoke. With lung cancer, therefore, the environmental factor (smoking) far outweighs the genetic predisposition. If we consider just populations of nonsmokers, then there may be some inherited predisposition to develop lung cancer. We can't tell if this inherited predisposition is genetic or not. It might represent a common environmental factor such as urban air pollution. A very careful study would be needed to determine whether there actually was a hereditary predisposition to lung cancer, apart from smoking, air pollution, and other known environmental carcinogens.
There are a few types of tumors where the mode of inheritance is known:
Von Recklinghausen's neurofibromatosis is a dominantly inherited condition which often results in skeletal deformity and the presence of many skin tumors and tumors of nerves. Ordinarily these tumors are benign, but there is a tendency for people with this disease to sometimes develop neurogenic sarcomas (cancers of the cells of the nerve sheath). There are people with this condition who have lived to a relatively old age. A similarly inherited disease is acoustic neuroma, in which people develop nerve sheath tumors of the nerve responsible for hearing, and deafness often results.
Retinoblastoma is transmitted by dominant gene and results in the development of tumors of the retina of the eye. These tumors appear early in childhood and result in the death of the child, unless the affected eye is removed.
Xeroderma pigmentosum is inherited as a recessive. This hereditary disease is characterized by a peculiar form of skin pigmentation, and the development of cancer of the skin on exposure to sunlight. The mystery of how it happens may be on the verge of being solved. There is a mechanism within the normal cell that is able to repair damage to DNA. Since DNA is continually damaged in the skin by ultraviolet radiation, the presence of this mechanism is essential to the maintenance of the genetic integrity of the skin cells. People with Xeroderma pigmentosum do not have this repair enzyme and cannot repair the damage done to their skin cells by ultraviolet radiation.
There is an inherited condition called Gardner's Syndrome, which predisposes people having this dominant gene to the development of polyps of the large intestine.. These polyps often undergo cancerous change.
These diseases constitute an almost complete list of cancerous and precancerous conditions in which the hereditary factors have been clearly characterized. With other conditions in which a familial disposition exists, no one knows what that familial disposition is due to.
A woman with a close relative having had breast cancer has about two to three times the chance of developing the disease as does someone with no family history of breast cancer. To give us some perspective, it should be pointed out that a woman who has never born children has at least twice the risk of developing breast cancer as one who has. Therefore, a woman with no family history of breast cancer, who has had no children, has about the same chance of developing breast cancer as a woman with a family history of breast cancer who has had three or more children. Of course, a woman with no family history of breast cancer can cut the risk in half if she has three or more children.
Scientists have been working for forty years on the tendencies of different strains of mice to develop cancer. With few exceptions, we still do not understand why only certain strains of mice develop certain types of tumors. There are many differences between mice and people, and to extrapolate directly from mouse to man at this stage of the game would be folly. I mentioned in a previous chapter that there is a strain of mice in which 100% of the animals will develop adrenal cancers if the ovaries are removed. No one has reported an equivalent situation in women. There is a strain of animals in which all of the animals develop leukemia; but no one has reported a family in which the incidence is anywhere near that high. In short, we just do not know enough about the inheritance of cancer.
Just because you inherit a susceptibility to a particular form of cancer is nothing to lose sleep over. If you were not susceptible to a particular form of cancer, you might be susceptible to early death, or heart disease, or stroke. We all have to die of something, and an inherited susceptibility to cancer is not all bad.
It is natural that someone who has lost his parents to heart disease should worry about contracting heart disease, and that someone who has lost parents or close relatives to cancer should worry about dying of cancer. Taking reasonable precautions makes sense, but cancerophobia can sometimes be as debilitating a disease as cancer itself.
A rational approach to the problem involves the recognition of the fact that an increased probability of developing a particular type of cancer does not mean that one will develop it. You must also recognize that a twofold or threefold increase In the frequency of breast cancer still means that a woman will probably not develop breast cancer, but will die of something else. We must also recognize that a good part of the mortality due to cancer is related to the patient not being treated early enough. Taking all of these factors into consideration, a family history of a particular type of cancer is nothing to lose sleep over. Women whose relatives have had breast cancer should examine themselves at frequent intervals; as should women whose relatives have not developed breast cancer. The same principle applies for all other forms of cancer. I am reminded of a man who had a family history of stomach cancer. He drank to calm his fears, and died of cirrhosis of the liver.