Modeling insight into spontaneous regression of tumors

Diagnostic radiation-induced regression of a metastatic primary intracranial germinoma: a case report

Pineal region germinomas are sensitive to radiotherapy. Standard neurosurgical management involves obtaining a tissue biopsy and to relieve the often accompanying obstructive hydrocephalus. We present a patient with a suspected hyper-radiosensitive metastatic primary intracranial germinoma where computed tomography scanning resulted in tumor regression before radiotherapy could be administered.

A Mathematical Model for the Onset of Avascular Tumor Growth in Response to the Loss of P53 Function

We present a mathematical model for the formation of an avascular tumor based on the loss by gene mutation of the tumor suppressor function of p53. The wild type p53 protein regulates apoptosis, cell expression of growth factor and matrix metalloproteinase, which are regulatory functions that many mutant p53 proteins do not possess. The focus is on a description of cell movement as the transport of cell population density rather than as the movement of individual cells. In contrast to earlier works on solid tumor growth, a model is proposed for the initiation of tumor growth. The central idea, taken from the mathematical theory of dynamical systems, is to view the loss of p53 function in a few cells as a small instability in a rest state for an appropriate system of differential equations describing cell movement. This instability is shown (numerically) to lead to a second, spatially inhomogeneous, solution that can be thought of as a solid tumor whose growth is nutrient diffusion limited. In this formulation, one is led to a system of nine partial differential equations. We show computationally that there can be tumor states that coexist with benign states and that are highly unstable in the sense that a slight increase in tumor size results in the tumor occupying the sample region while a slight decrease in tumor size results in its ultimate disappearance.

Regression of Pineal Lesions: Spontaneous or Iatrogenic? A Case Report and Systematic Literature Review

BACKGROUND

Tumors arising from the pineal region account for approximately 1% of intracranial neoplasms. We present a case of a previously healthy 5-year-old boy with an acute onset of headache. A magnetic resonance imaging (MRI) scan showed a pineal mass with aqueduct compression. The patient was scheduled for tumor resection. An endoscopic third ventriculostomy was performed in advance for the treatment of hydrocephalus. Afterwards, MRI showed a relevant regression of the pineal mass without specific treatment. Consequently, surgery was cancelled and further MRI follow-up showed a regression of the mass and a constant tumor mass over a period of 30 months. Spontaneous regression of malignant tumors is a rare phenomenon with an incidence of 1 of 60,000-100,000 cases. Only a few cases with spontaneous regression of pineal tumors have been reported.

METHODS

We performed a systematic literature review according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) guidelines on spontaneously regressing pineal lesions and found 13 cases in the literature.

RESULTS

Six hypotheses for explaining tumor regression were found, comprising treatment with steroids, effects of diagnostic irradiation, treatment of hydrocephalus, pineal apoplexy, surgical trauma, and immunologic mechanisms. None of these mechanisms was evidentiary. However, in all reported cases, some kind of treatment (e.g. treatment of hydrocephalus, application of steroids, and so on) has been performed before tumor regression.

CONCLUSIONS

The clinician has to bear in mind that regression of pineal tumors might be triggered by use of steroids, for example, and in cases of improvement of the patient's presenting symptoms, new MRI scans should be performed.

Stochastic dynamics and the evolution of mutations in stem cells

Stem cells are the target of mutations that can lead to life threatening diseases. However, stem cell populations tend to be small and therefore clonal expansion of mutant cells is highly sensitive to stochastic fluctuations. The evolutionary dynamics of mutations in these cells is discussed, taking into consideration the impact of such mutations on the reproductive fitness of cells. We show how stochastic effects can explain clinical observations, including extinction of acquired clonal stem cell disorders.

Extinction kinetics for metastatic cancer stem cells

PURPOSE

Cancer Stem Cells (CSC) are hypothesised to influence tumour growth through their self-replication, cell loss, and differentiation into growth-limited cell types. A model for the random gain and loss of metastatic CSC is developed to investigate how the balance between these processes might affect metastatic efficiency, tumour involution and treatment response.

MATERIALS AND METHODS

A stochastic birth-death model for metastasis was constructed for the replication and loss of CSC. The model was extended to account for single and sequential cancer treatments, with CSC repopulation.

RESULTS

If CSC losses exceed gains, the metastasis would become extinct. The resultant extinction probability was greatest during a period of stochastic susceptibility; treatment could extend, or reestablish, this period.

CONCLUSION

Random CSC losses, with 'seed and soil' selection, provided a mechanistic explanation for the involution of metastases, as well as for metastatic inefficiency. With such background losses, and the growth limitations of differentiated cells, a metastasis could take years to reach macroscopic size. The susceptibility period could be protracted, providing for a window for therapeutic opportunity. Metastases with a high background CSC loss would be more responsive to treatment than stabler metastases. Modulation of this loss could enhance the efficacy of conventional cancer treatment.

Regression of primary central nervous system germinoma after dexamethasone administration: a case report

Childhood central nervous system (CNS) germinoma are highly curable brain tumors characterized pathologically by varying degrees of lymphocytic infiltration. The authors present a case of a CNS germinoma with significant regression in size following surgery and administration of dexamethasone, prior to initiation of chemotherapy or irradiation. The authors speculate the possible mechanism involved in its occurrence. Perioperative corticosteroid administration in patients with CNS germinoma may obfuscate the increase in response demonstrated with various chemotherapy regimens or with irradiation in CNS germinomas.

Spontaneous regression of a breast carcinoma: a case report

Spontaneous regression of malignant tumors is a rare event. It is defined as partial or total disappearance of a proven malignant tumor without adequate medical treatment. The causes of this phenomenon are various. Nevertheless, malignant tumors do regress occasionally for no apparent reason, as evidenced by many clinical observations. We report a case of a 68-year-old woman, who was presented with a several-month history of a painless firm lump, initially of 1 cm in diameter and growing to a large solid regular tumor of 2.5 x 2.5 cm in size, in the upper outer quadrant of her right breast. Preoperative histopathological diagnosis revealed ductal invasive carcinoma. Later on, while awaiting surgical treatment, she suffered an arm injury requiring a 1-month delay of surgery. After recovery, on the date of surgery the tumor disappeared, and, in addition, it was not found in tissue specimens obtained from quadrantectomy. After 78 months of follow-up there was no evidence of relapse. In this report, we discuss clinical and histopathological findings, patient management and possible mechanisms of cancer regression.

Prolonged perturbation of the oscillations of hepatoma Fao cell proliferation by a single small dose of methotrexate

The proliferation rate of various cell types in vitro, including hepatoma Fao cells, displays aperiodic oscillations. The frequency of these oscillations is about one every 3-5 weeks, and there are variations in cell functions and polarity. Topological analysis has showed that these oscillations in growth rate are determined, and presumably chaotic. One characteristic of complex chaotic systems is that their dynamics can be persistently modified by a small external perturbation. We show that treatment with a single small dose of the anticancer drug methotrexate causes long-term stable alteration of the oscillatory dynamics of Fao cell proliferation. The oscillations of growth rate are shifted, and their mean level decreased according to a fractal pattern.

Genetic analysis of the growth curve of Rous sarcoma virus-induced tumors in chickens

White Leghorn chicks homozygous for B19 MHC haplotype were selected for 18 generations on tumor regression after inoculation in the wing web with an SR-D strain of Rous sarcoma virus (RSV) at 4 wk of age. Each chick was assigned a tumor profile index (TPI) based on age at death and size of the tumor. During 18 generations, 2,010 birds were divergently selected on TPI for either progression or regression of the tumor (P and R lines). A Brody growth curve was fitted for each bird. Brody function parameters included the asymptotic tumor volume (A), the factor for increased growth in progression phase (K1), the factor for decreased growth in regression phase (K2), age at maximum volume (Tmax), and maximum volume of the tumor (Vmax). Tumor growth curves were found to be different according to line, sex, and restriction fragment pattern Y complex Rfp-Y MHC haplotype (Yw*15, Yw*16, and Yw*17). Within the P line, birds from the Yw*16 haplotype reached Vmax at an earlier age than Yw*15 and Yw*17, but with a lower Vmax value. Within the R line, tumor growth curves of birds from Yw*16 and Yw*17 haplotypes were similar. Rank correlations between the different parameters and TPI were low (between -0.26 and 0.36). Heritability estimated by the sire component was high for Vmax (0.73). Heritabilities of Tmax and K2 were moderate (0.20 to 0.23 for Tmax and 0.18 to 0.21 for K2) allowing these traits to be used as selection criteria. Heritabilities of A and K1 were lower than 0.12. Modeling the growth curve should contribute to better distinction between progressors and regressors.

Markovian chemicals "in silico" design (MARCH-INSIDE), a promising approach for computer-aided molecular design I: discovery of anticancer compounds

A simple stochastic approach, designed to model the movement of electrons throughout chemical bonds, is introduced. This model makes use of a Markov matrix to codify useful structural information in QSAR. The self-return probabilities of this matrix throughout time ((SR)pi(k)) are then used as molecular descriptors. Firstly, a calculation of (SR)pi(k) is made for a large series of anticancer and non-anticancer chemicals. Then, k-Means Cluster Analysis allows us to split the data series into clusters and ensure a representative design of training and predicting series. Next, we develop a classification function through Linear Discriminant Analysis (LDA). This QSAR discriminates between anticancer compounds and non-active compounds with a correct global classification of 90.5% in the training series. The model also correctly classified 86.07% of the compounds in the predicting series. This classification function is then used to perform a virtual screening of a combinatorial library of coumarins. In this connection, the biological assay of some furocoumarins, selected by virtual screening using the present model, gives good results. In particular, a tetracyclic derivative of 5-methoxypsoralen (5-MOP) has an IC50 against HL-60 tumoral line around 6 to 10 times lower than those for 8-MOP and 5-MOP (reference drugs), respectively. Finally, application of Iso-contribution Zone Analysis (IZA) provides structural interpretation of the biological activity predicted with this QSAR.

p53 expression and apoptosis in melanomas of dogs and cats

Twenty-seven melanocytic tumours from 20 dogs and four cats were examined for p53 expression and apoptosis. They included tumours that were histologically classified as benign (BM), primary malignant (PMM) and metastatic malignant melanomas (MMM). For all cases clinical follow-up was available. p53 expression was examined immunohistochemically using different monoclonal and polyclonal antibodies. Apoptosis was detected using the TUNEL technique. The tissue sections were analysed using a quantitative image analysing system. A p53 index (p53I) and an apoptotic index (AI) were determined. p53 over-expression was found infrequently in these canine and feline melanocytic tumours. Apoptosis was observed in some of the malignant tumours. In one feline case of malignant melanoma, p53 accumulation together with apoptosis was seen in three metastases but not in the primary tumour. p53I and AI were not significantly correlated with survival. These results are similar to those reported for human cutaneous melanomas.

Stochastic modeling in toxicokinetics. Application to the in vivo micronucleus assay

A stochastic model for the in vivo micronucleus assay is presented. This model describes the kinetic of the rate of micronucleated polychromatic erythrocytes induced by the administration of a mutagenic compound. For this, biological assumptions are made both on the erythropoietic system and on the mechanisms of action of the compound. Its pharmacokinetic profile is also taken into account and it is linked to the induced toxicological effect. This model has been evaluated by analyzing the induction of micronuclei is mice bone marrow by a mutagenic compound, 6-mercaptopurine (6-mp). This analysis enabled to make interesting remarks about the induction of micronuclei by 6-mp and to put to light an unsuspected wavy kinetic by optimizing the experimental design of the in vivo micronucleus assay.

A dynamical model for the growth and size distribution of multiple metastatic tumors

Metastasis is the spread of tumors culminating in the establishment of one or more secondary tumors at remote sites. In deciding the best treatment for cancer therapy, estimations of the colony size of metastatic tumors and predictions of the future spread of colonies are needed. A dynamical model for the colony size distribution of multiple metastatic tumors is presented here. The dynamics is described by equations that incorporate both the colonization by metastasis and the growth of each colony. When the colony growth is subject to the Gompertz function, the explicit solution obtained tends to an asymptotic stable distribution that shows a monotonically decreasing or U-shaped pattern according to the values of clinically significant parameters, such as the colonization coefficient and the fractal dimension of blood vessels. This predicted colony size distribution agrees well with successive data of a clinically observed size distribution of multiple metastatic tumors of liver cancer. The combined analysis of the theoretical colony size distribution and clinical data will give useful information on the diagnosis and the therapy for cancer patients.