It is generally believed that cancer is not one disease, but is, instead, a group of complex malignant processes. The most widely accepted theory is that every cancer begins from changes in a single cell and that most neoplasms develop gradually. With advancing age the chances of developing cancer increase. However, cancer is not a problem of old age alone; it is also a problem of childhood.

Causes of Cancer

The cause or causes of cancer are still unknown. What makes some people more susceptible to cancer than others? For example, certain urban dwellers are exposed to air containing many carcinogens ; but why is it that not all of them develop cancer? Scientists from many fields are concerned with the search for those factors responsible for the onset of cancer and which, if eliminated, will prevent malignant changes even if other carcinogenic factors are present.

The geneticist studies the genes that determine heredity, trying to find out whether or not they provide factors which increase or decrease our susceptibility to cancer. The neoplastic process may result from a change or series of changes in the hereditary mechanisms of the cell. What happens in the cellular development of the small percentage of very young children who are susceptible to the eye cancer called retinoblastoma?

These are but a few of the unanswered questions to which much scientific effort is being directed.

Transmission of cancers in purebred strains of mice enables scientists to study certain types of cancer. But man is not an inbred creature that permits strong hereditary tendencies to cancer to appear, and many scientists think hereditary influences related to human cancer are slight. However, a few conditions such as retinoblastoma, multiple polyposis, and multiple neurofibromatosis are generally considered of hereditary origin.

The endocrinologist is seeking to determine the relationship of hormones to the development, cause and progression of cancer.

We know that many of our bodily processes are regulated by hormones produced by such glands as thyroid, pituitary, adrenals, ovaries, and testes. There is accumulating evidence that changes in hormone function are linked to cancer of the breast.

In laboratory experiments the virologist has found viruses that cause cancer in a wide range of animal species and also viruses that destroy cancer. There are numerous studies in progress to determine whether there is a relationship between viruses and human cancer. If a virus is a cause of cancer it must become activated under certain conditions. This may be similar to the Herpes virus that causes cold sores; it stays dormant until something "triggers" it to action.

Men in several scientific disciplines are studying human exposure to natural and manmade carcinogens that may incite cancer over a period of time. A carcinogen is usually defined as any cancer inciting substance. There are several hundred substances in our environment known to have carcinogenic properties. For instance, overexposure to X-ray or radium may cause skin cancer to develop. Excessive exposure to sunlight, especially in fair-skinned persons, may also produce skin cancer.

Evidence now points strongly to cigarette smoking as a factor in the development of lung cancer, especially among long-time-heavy smokers.

These seemingly unrelated lines of investigation are merging now that medical research has yielded a wealth of information on the role of nucleic acids in the life and death of cells. DNA (see glossary) in particular is receiving much attention. DNA is of special interest because of its role in cancer chemotherapy and because it may possibly be involved in the conversion of normal cells into malignant cells. Modern cancer research covers only about 50 years and, like that of other biologic investigations, has progressed from the mere observation of natural phenomena to active experimental procedures.

From time to time the role of trauma as a cause of cancer is raised for discussion. Scientists generally agree that a single trauma to normal tissue does not produce cancer. However it is believed that chronic irritation to a susceptible area may sometimes initiate or accelerate the development of a malignancy.