Darwinian medicine: a case for cancer

MC1R variants associated susceptibility to basal cell carcinoma of skin: interaction with host factors and XRCC3 polymorphism

The variants within the human melanocortin 1 receptor (MC1R) gene are associated with an increased risk of different skin cancers. In this study, we genotyped by direct sequencing, 529 cases of basal cell carcinoma of the skin (BCC) and 533 healthy controls for polymorphisms in the entire MC1R gene. In addition to 10 common polymorphisms, we detected 23 rare variants in the gene. The presence of any nonsynonymous MC1R variant was associated with an increased risk in the carriers (odds ratio OR 1.66, 95% confidence interval CI 1.28-2.14) corresponding to a population attributable fraction of about 27%. The odds ratio for the risk in the carriers of 2 MC1R variants was 2.69 (95% CI 1.77-4.08). The risk of BCC in the carriers of MC1R variants with fair complexion was almost twice as much as in the corresponding noncarriers. The carriers of the R163Q variant with a medium skin complexion were at a 3-fold higher risk than the noncarrier counterparts. The interaction, of effect on the BCC risk, between the MC1R variants and types of skin response to sun exposure was greater than multiplicative. We also observed a multiplicative interaction of risk due to the MC1R variants and the common allele (high risk) of the T241M polymorphism in the XRCC3 gene. Our data confirmed the status of the nonsynonymous MC1R variants as independent genetic risk factors for BCC. However, the mechanism through which the variants influence the risk likely involves complex interactions with other genetic and host risk factors.

The age incidence of childhood B-cell precursor acute lymphoblastic leukemia in Mexico City

The objective of this population-based survey was to assess the peak age of incidence of B-cell precursor acute lymphoblastic leukemia (ALL) in children in Mexico City (MC). All patients were classified according to their immunophenotype, and only B-cell precursor and T-lineage were analyzed. Rates of incidence were calculated x10 children. Of the 364 children from MC who were included in this study, immunophenotyping had been performed for 81.6%. The frequency of B-cell precursor ALL was 76.1%, whereas T lineage ALL showed a frequency of 23.6%. Peak age for ALL was 2 to 3 years of age. B-cell precursor ALL was the major contributor to peak age; T lineage ALL showed a peak among 1 and 3 years of age. We conclude that the age peak for children with ALL in MC is within the ranges reported for developed countries and that B-cell precursor ALL is the main contributor to these peak.

Declining cellular fitness with age promotes cancer initiation by selecting for adaptive oncogenic mutations

Age is the single most important prognostic factor in the development of many cancers. The major reason for this age-dependence is thought to be the progressive accumulation of oncogenic mutations and epigenetic changes. Similarly, mutagens are thought to be carcinogenic primarily by engendering oncogenic mutations. Yet while the accumulation of heritable somatic changes is expected to augment the incidence of oncogenic mutations, a major effect of increased mutation load is reduced fitness. We propose that the fitness of progenitor cell compartments substantially impacts on the selective advantage conferred by particular mutations. We hypothesize that reduced cellular fitness within aged stem cell pools can select for adaptive oncogenic events and thereby promote the initiation of cancer. Thus, certain oncogenic mutations may be adaptive within aged but not young stem cell pools. We further argue that accumulating genetic alterations with age or mutagen exposure might promote cancer not only by causing oncogenic hits within cells but also by leading to eventual reduction in stem cell fitness, which then selects for oncogenic events. Therefore, initial stages of cancer development may not be limited by the incidence of initiating oncogenic changes, but instead by contexts of reduced cellular fitness that select for these changes.

Clinical and biological significance of HLA-G expression in ovarian cancer

Ovarian cancer is the most lethal gynecologic neoplastic disease in which the molecular etiology remains largely unclear. Like other cancer types, evolution of ovarian tumor cell species is accompanied by acquisition of novel gene products and these new tumor-associated antigens elicit a host immune response that creates selection pressure upon the emerging tumor clones. One of the mechanisms that ovarian cancer cells evade immune surveillance is by upregulating human leukocyte antigen-G (HLA-G) expression. HLA-G is a non-classical MHC class I molecule and accumulated evidence has suggested its biological role in inactivating immune response. It has been well known that HLA-G expression is frequently detected in the most aggressive type of ovarian cancer, i.e., high-grade serous carcinoma, and measurement of HLA-G protein levels has shown promise for detection and prognosis prediction in ovarian cancer. This review summarizes those recent studies on HLA-G expression in ovarian cancer with special focus on its clinical and biological significance which is fundamental to elucidate the molecular mechanisms in ovarian cancer development and paves the foundation for future HLA-G-based diagnostics and therapeutics.

Biological stoichiometry in human cancer

Background

A growing tumor in the body can be considered a complex ecological and evolutionary system. A new eco-evolutionary hypothesis (the “Growth Rate Hypothesis”, GRH) proposes that tumors have elevated phosphorus (P) demands due to increased allocation to P-rich nucleic acids, especially ribosomal RNA, to meet the protein synthesis demands of accelerated proliferation.

Methodology/Principal Findings

We determined the elemental (C, N, P) and nucleic acid contents of paired malignant and normal tissues from colon, lung, liver, or kidney for 121 patients. Consistent with the GRH, lung and colon tumors were significantly higher (by approximately two-fold) in P content (fraction of dry weight) and RNA content and lower in nitrogen (N):P ratio than paired normal tissue, and P in RNA contributed a significantly larger fraction of total biomass P in malignant relative to normal tissues. Furthermore, patient-specific differences for %P between malignant and normal tissues were positively correlated with such differences for %RNA, both for the overall data and within three of the four organ sites. However, significant differences in %P and %RNA between malignant and normal tissues were not seen in liver and kidney and, overall, RNA contributed only ∼11% of total tissue P content.

Conclusions/Significance

Data for lung and colon tumors provide support for the GRH in human cancer. The two-fold amplification of P content in colon and lung tumors may set the stage for potential P-limitation of their proliferation, as such differences often do for rapidly growing biota in ecosystems. However, data for kidney and liver do not support the GRH. To account for these conflicting observations, we suggest that local environments in some organs select for neoplastic cells bearing mutations increasing cell division rate (“r-selected,” as in colon and lung) while conditions elsewhere may select for reduced mortality rate (“K-selected,” as in liver and kidney).

Natural antibodies and cancer

Immunity is not only responsible for recognition and elimination of infectious particles, but also for removal of cellular waste, modified self structures and transformed cells. Innate or natural immunity acts as a first line defense and is also the link to acquired immunity and memory. A striking phenomenon of immunity against malignant cells is that neither in animals nor in humans affinity-maturated tumor-specific IgG antibodies have been detected so far. All tumor-specific isolated antibodies were germ-line coded natural IgM antibodies. It's also a fact that these IgM's preferentially bind to carbohydrate epitopes on post-transcriptionally modified surface receptors and that they all induce a cancer-specific apoptosis, by triggering the intrinsic apoptotic pathway. From an evolutionary point of view, this makes sense because cancer cells are not infectious, so there is no need for memory. Natural IgMs bind to conservative structures because they are coded by a limited set of genes and they use apoptosis, the "clean" way of killing, to avoid inflammatory processes.