The complex liaison between cachexia and tumor burden (Review).

Cachexia is a wasting syndrome that afflicts end-stage cancer patients. Whereas a consensus statement for a definition of cachexia recently has been accomplished, a useful measurement for this condition at present is lacking. The aim of the present review is to discuss the advantage of introducing the measurement of tumor burden for a better overall evaluation of cachexia. Our suggestion ensues from a somewhat novel perspective in the field of infectious disease research where a careful measurement of the pathogen load, between i.e. different host genotypes, leads to the definition of the concept of tolerance to the infectious insult. Indeed tolerance concurs, together the more classical resistance, in maintaining the host reproductive fitness or health state. Noticeably a similar reasoning may apply to tumor biology as well. Whereas the extent of cachexia increases with tumor burden, the relationship between these two correlates of tumor progression fluctuates in a broad range. We have selected from the literature studies in the rodent model where significant variation in the course of the wasting illness during cancer was observed and quantitatively assessed comparing experimental groups marked by different genotype, drug treatment, diet or gender. These studies may be further classified in two categories: the former where the experimental condition associated to milder cachexia is accompanied to a lesser tumor burden, the latter where the inhibition of cachexia results disentangled from the tumor burden, that is the whole number of cancer cells results unchanged or even, paradoxically, is increased. In addition we survey, even in the context of human malignancy, the significance and feasibility of plotting quantitative estimates of cachexia against the whole tumor burden. Ultimately, the principal endeavor of introducing the measurement of tumor burden, in both experimental and clinical oncology, may be to achieve a better assessment of the inter-individual variation in the host vulnerability to cancer cachexia.