pathological changes that precede the development of a malignant tumor.

The concept of “precancer” was first formulated with regard to skin cancer, which is the most accessible to clinical observation. Later, precancer was diagnosed in the lower lip, breasts, cervix of the uterus, and stomach. Research in experimental oncology has demonstrated that precancerous conditions differing in clinical manifestations represent the same basic pathological process with the same definite pattern.

There are three stages of precancer generally distinguished in Soviet oncology. In the stage of uneven diffuse hyperplasia, the tissue retains its normal structure, but the number of its structural elements, such as cells and fibers, increases. In the stage of focal proliferation, the total mass of multiplying cells contains areas, or foci, in which the cells divide with unusual rapidity. In the comparatively benign tumor stage the foci of multiplying cells steadily cease to resemble the original tissue and become increasingly isolated but do not exhibit a tendency toward invasive growth—that is, growth into and destruction of healthy tissue. The first stage is not yet precancer in the strict sense of the word. The second stage is the most characteristic stage of a precancer. The third stage is not essential, since the cancer can bypass it and continue developing. A precancer can regress or cease developing for a long time.