Precancers are the lesions from which cancers grow. Some people question why we need to specify some lesions as precancers when we know that carcinogenesis is a multistep process and that every cancer traverses many un-named biological states as it develops into a fully malignant lesion. Why can't we recognize that precancers are just an early form of cancer and refer to the precancers by the name of its developed cancer? Can't we just use adjectives like "early stage" squamous carcinoma or "non-invasive" pancreatic carcinoma? Wouldn't that make life a lot easier than inventing names for the pre-invasive stage of every cancer?
Much as I like data simplification, it just can't be done in the case of the precancers. Precancers have specific, characteristic properties that separate them from cancers. Because of these properties, the treatment of precancers may be very different from the treatment of cancers. In fact, if we take full advantage of the biologic features that separate the precancers from the cancers, we may actually find that we can eliminate deaths from cancer.
What are these special properties of the precancers?
1. Precancers, unlike cancers, tend to regress. Cancers tend to grow and only rarely regress. Furthermore, it some cases, we can influence the rate of regression of the precancers with relatively non-toxic drugs. Understanding the biology of regression is something that we can only learn from the precancers.
2. When a precancer progresses, it progresses to cancer. But not all precancers progress. Many precancers just stay precancers indefinitely, as far as we can tell. Why should we think of a precancer as an early stage of a cancer if it never becomes a cancer?
3. Precancers that progress to cancer can apparently progress into more than one type of cancer. Consequently, there are more types of cancers than there are types of precancers. For instance, in the lung, squamous metaplasia/dysplasia of bronchial epithelium may give rise to bronchogenic squamous cell carcinoma, bronchogenic adenocarcinoma, bronchogenic small cell carcinoma, or bronchogenic mixed carcinoma. If a lesion can progress into any of several different lesions, it is impossible to pretend that the lesion is just an early form of one named cancer.
4. Precancers can be cured. When a precancer is cured, the cancer never develops. The treatments that we use for precancers are likely to be different from (and much less toxic than) the treatments that we use for cancers.
Because the biology of precancer is distinguishable from the biology of cancer, and because there are clinically useful reasons (i.e., treatment and prevention of cancer) to make these distinctions, the precancers should be curated as designated entities.