The incidence of hematologic tumours: a cellular model for the age dependence

Chemotherapy in conjoint aging-tumor systems: some simple models for addressing coupled aging-cancer dynamics

Background

In this paper we consider two approaches to examining the complex dynamics of conjoint aging-cancer cellular systems undergoing chemotherapeutic intervention. In particular, we focus on the effect of cells growing conjointly in a culture plate as a precursor to considering the larger multi-dimensional models of such systems. Tumor cell growth is considered from both the logistic and the Gompertzian case, while normal cell growth of fibroblasts (WI-38 human diploid fibroblasts) is considered as logistic only.

Results

We demonstrate, in a simple approach, how the interdependency of different cell types in a tumor, together with specifications of for treatment, can lead to different evolutionary patterns for normal and tumor cells during a course of therapy.

Conclusions

These results have significance for understanding appropriate pharmacotherapy for elderly patients who are also undergoing chemotherapy.

On the role of aging in carcinogenesis

Correlation coefficients for age-standardized incidence rates between cancers of the stomach, colon, rectum and lung over place (worldwide) and time (in Connecticut) vary from positive to negative values, indicating that these cancers are not caused by common environmental agents. Correlation coefficients for age-incidence patterns (the variation in age-specific rates with age) between these cancers, on the other hand, are all highly positive for both sexes. We conclude that the carcinogenic determinants that vary with age are common to the cancers studied and to both sexes, and distinct from the carcinogenic determinants that vary with place and time. For the cancers studied, incidence rates are negligible until age 30, at which time they increase dramatically and continue to increase at least until age 75. The rate of increase, however, diminishes continuously with advancing age after 30. We suggest that the role of aging in cancer incidence is determined by two components, one responsible for the dramatic rate increase beginning near age 30 and one responsible for the gradual diminution in that rate increase. The former may correspond to the activation of quiescent cells with damaged DNA or to the deactivation of DNA surveillance or repair or to impaired apoptosis, while the latter may correspond to the loss of cell division potential.

Cellular proliferation and genetic events involved in the genesis of Burkitt lymphoma (BL) in immune compromised patients

A mathematical model simulating lymphomagenesis based on the two-hit theory of carcinogenesis is presented by contrasting the biologic variables responsible for a high risk of developing Burkitt lymphoma (BL) in three immunosuppressed groups with that of nonendemic BL. In this model, the pro-B lymphocyte is considered to be the target for BL-specific translocations such as t(8;14). With repeated mitosis, the target cell pool expands in the high-risk individual, and, thereby, the opportunities for a spontaneous translocation to arise are increased. The chromosomal translocation endows the target cell with survival advantages, and, hence, lymphoma develops. Modeling results demonstrate that this increased cell proliferation is sufficient in accounting entirely for the increase in tumor prevalence. Preventing enhanced cellular proliferation by obviating immune deficiency and treating patients with agents that restore immunity or have antiviral and antiproliferative properties prior to conversion from polyclonal B-cell proliferation to monoclonal malignancy could obviate the development of BL.

Cancer and aging

It is widely accepted that the incidence of cancer increases with aging and many hypotheses have been put forward to explain this association. A review of the literature, however, shows that the relationship between cancer and aging has to be reappraised. Although the incidence of most cancers increases during the second half of the animal life span, only with a few does it increase progressively with senescence in humans as well as in animals. As a matter of fact in many cases the incidence does not vary, levels off or even decreases in old individuals. Late developing tumors also seem in many instances to progress more slowly. Thus it seems that the incidence of cancer is related to age rather than to aging and that some conditions may be created during senescence which oppose the development of some cancers.

On the role of aging in cancer incidence: an interpretation of the prostate cancer anomaly with implications for routine screening

Cross-sectional age-incidence patterns for the common male and female cancers in Connecticut were normalized to describe the percentage of total incidence that occurred at each age. The pattern for prostate cancer was atypical--less than the 99% confidence limit from the mean at ages less than 60 and greater than the 99% confidence limit from the mean at ages greater than 75. The available international data on latent carcinoma of the prostate, when normalized as above, resembled the mean male and female cancer patterns in Connecticut and suggested that the atypical behavior of clinical prostate cancer was the result of a lag between the incidence of latent carcinoma and promotion to clinical disease. Confirmation of this suggestion, with the potential to distinguish epidemiologically those latent carcinomas that remain asymptomatic from those that progress to malignancy, awaits routine screening for the latent carcinoma.