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Definition and classification of cancer: monothetic or polythetic?
1Unit of Cancer Epidemiology, Main Hospital, Torino, Italy.
Abstract:
Since the microbiological revolution, most infectious diseases have been defined and classified according to an etiologic criterion, i.e. the identification of single, external "necessary" causes (for example, Mycobacterium for tuberculosis). This is not the case with cancer. Not only external "necessary" causes of cancer have not been identified, but also the morphological classification cannot be based on univocal criteria. Although "neoplasia" and "anaplasia" appear to be universal attributes of cancer, these events are only quantitative. Neoplastic growth can be fast or slow (development may take weeks or years), and tissue pathologies are difficult to detect from normal tissue in some cancers but are obvious in others. Common special properties of anaplasia appear to be concealed in the wide range of morphologies. In the absence of a coherent morphological definition, and of external necessary causes (such as bacteria for infectious diseases), a mechanistic definition could be adopted. However, unless molecular biology discovers specific mechanistic steps in carcinogenesis, which indicate the existence of "necessary" events in carcinogenesis, we cannot adopt a univocal (monothetic) definition of cancer. The alternative is to use a polythetic definition, according to Wittgenstein's model of a "long rope twisted together out of many shorter fibres."
Insights
Cancer lacks a single cause or clear definition, unlike infectious diseases. This study explores defining cancer through a polythetic approach, acknowledging its complex and varied nature.
Area of Science:
- Oncology
- Pathology
- Philosophy of Science
Background:
- Infectious diseases are defined by specific etiologic agents (e.g., Mycobacterium for tuberculosis).
- Cancer lacks identified external "necessary" causes and a universally applicable morphological classification.
- Current cancer attributes like neoplasia and anaplasia are quantitative and variable, not definitive.
Purpose of the Study:
- To address the challenge of defining cancer in the absence of a single etiologic cause or clear morphological criteria.
- To explore alternative definitions for cancer beyond traditional monothetic (single criterion) approaches.
- To propose a polythetic definition for cancer, drawing parallels with Wittgenstein's concept of family resemblances.
Main Methods:
- Comparative analysis of disease definition criteria (etiologic vs. morphological vs. mechanistic).
- Review of established concepts in cancer biology, including neoplasia and anaplasia.
- Application of philosophical models of definition (monothetic vs. polythetic) to cancer classification.
Main Results:
- Cancer cannot be defined by a single "necessary" external cause, unlike most infectious diseases.
- Morphological classifications of cancer are not univocal due to wide variations in appearance and detectability.
- Quantitative attributes like neoplastic growth rate and anaplasia exhibit significant variability, hindering a strict definition.
Conclusions:
- A monothetic definition of cancer is currently not feasible due to the lack of identified specific mechanistic steps in carcinogenesis.
- A polythetic definition, encompassing a range of characteristics without requiring all to be present in every case, is a more suitable model for cancer.
- This approach acknowledges the complex, multifactorial nature of cancer, akin to a "long rope twisted together out of many shorter fibres".