Abstract
Is cancer a natural kind? On the one hand, the question is whether we are right to split cancer into the categories we use. According to Plutynski (([2018]), cancer nosology yields “a multimodal and cross-cutting family of classificatory schemes” which seems to warrant “pluralist realism” about cancer. On the other hand, the question is whether our concept of ‘cancer’ simply lumps together facts according to human interests, which does not allow for useful generalizations. Cancer anthropocentrism is challenged by a rising approach in oncology, namely comparative oncology, which investigates cancer in all species (e.g., (Aktipis et al. [2015]; Schiffman and Breen [2015]; Albuquerque et al. [2018]). According to its proponents, a major advantage of this approach is that it frees us from human practical biases and yields better generalizations about cancer (Aktipis [2020]), indeed even leading to a “universal theory of cancer biology” (Dujon et al. [2021]). What can we hope to learn from the nonanthropocentric approach of comparative oncology? Although comparative oncology can challenge our category of cancer, it is itself fraught with the problem of which phenomena should count as cancer. Some researchers are very inclusive and take any tumor to be cancer, including in invertebrates and plants; others prefer to limit the category to what can invade other tissues and metastasize. Criteria and extension of cancer are clearly interdependent, which often gives the impression of a certain arbitrariness in comparative oncology (what people find is a direct reflection of the definition of cancer they started with). To break this circle, we argue that it is better to embrace a provisional and heuristic anthropocentrism, which begins with hypothetical generalizations about human cancers. Human cancers may be special, but they are the best-known cancers. Precise hypotheses relative to these generalizations can then be tested in other species. We propose in particular to identify “comparative paradoxes”, i.e., claims about cancer that should hold in various species, but actually do not hold. For instance, Peto’s paradox is the puzzle of why large organisms don’t get cancer more often than small ones. The implicit generalization is that disordered cells should be proportional to the number of cells, given that cancer is caused by the accumulation of random mutations in individual cells, but this is precisely what observation contradicts (Abegglen et al., 2015). Whenever this generalization does not hold and the explanation does not reside in the fact that some animals have evolved highly specific anticancer mechanisms, it has the potential to challenge our most general conceptions of cancer. In addition to Peto’s paradox, we will discuss two other paradoxes: the connection between cancer and longevity and the immunological control over cancer. Prominent authors in comparative oncology have argued that the main advantage of this approach is to reconceptualize cancer as a much broader phenomenon: cancer is best understood as a form of “cheating” (Aktipis et al 2015). Instead, we claim that its main advantage is to assess and revise our most entrenched convictions about how cancer works.
