Læknablaðið : fylgirit - 01.06.1982, Síða 35

22
PLENARY LECTURE
ENVIROMENTAL FACTORS AMONG CAUSES OF CANCER
Hrafn Tulinius, Icelandic Cancer registry
Summary: Terms relating to causation of cancer are discussed.
The environmental factors are defined as those influences,
which originate in the environment, and have an effect on the
organism during its lifetime. Multifactorial causation is
of great importance in cancer etiology. A cause and causes,
including a sufficient cause, a component cause and a
necessary cause are discussed. Neoplastic diseases are a
heterogeneous group with certain things in common. The cause
of neoplastic diseases that are known can be classified into
broad categories. These are, culture or way of life, bio-
logical agents, physical agents, and chemical substances. It
is sometimes assumed that those cancers, that are more
frequent in the western world than elsewhere, and increase
in frequency, are due to the western way of life. These
include many common types such as carcinoma of breast,
prostate, colon and lung.
Unequivocal proof, that viruses cause human cancers is still
lacking, but they can cause cancers in experimental animals.
Schistosoma haematobium infestation is strongly associated
with squamous cancers of the urinary bladder.
Irradiation is well documented as a cause of various types
of leukemias and cancer. Several chemical substances are
known to cause human cancer. Among the best known are some
colouring substances that cause urinary neoplasms, aflatoxin
which causes liver-cancer, certain drugs, and the group of
chemical substances called N-nitroso compounds. Examples
illustrating these categories are given.