Compared with transplanted
tumor models or genetically engineered
cancer models, chemically induced primary
malignancies in experimental animals can mimic the clinical
cancer progress from the early stage on.
Cancer caused by chemical
carcinogens generally develops through three phases namely initiation, promotion and progression. Based on different mechanisms, chemical
carcinogens can be divided into genotoxic and non-genotoxic ones, or complete and incomplete ones, usually with an organ-specific property. Chemical
carcinogens can be classified upon their origins such as
environmental pollutants, cooked meat derived
carcinogens, N-
nitroso compounds,
food additives,
antineoplastic agents, naturally occurring substances and synthetic
carcinogens, etc.
Carcinogen-induced models of primary
cancers can be used to evaluate the diagnostic/
therapeutic effects of candidate drugs, investigate the biological influential factors, explore preventive measures for carcinogenicity, and better understand molecular mechanisms involved in
tumor initiation, promotion and progression. Among commonly adopted
cancer models, chemically induced primary
malignancies in mammals have several advantages including the easy procedures, fruitful
tumor generation and high analogy to clinical human primary
cancers. However, in addition to the time-consuming process, the major drawback of chemical
carcinogenesis for translational research is the difficulty in noninvasive
tumor burden assessment in small animals. Like human
cancers,
tumors occur unpredictably also among animals in terms of timing, location and the number of lesions. Thanks to the availability of magnetic resonance imaging (MRI) with various advantages such as ionizing-free scanning, superb soft tissue contrast, multi-parametric information, and utility of diverse
contrast agents, now a workable
solution to this bottleneck problem is to apply MRI for noninvasive detection, diagnosis and therapeutic monitoring on those otherwise uncontrollable animal models with primary
cancers. Moreover, it is foreseeable that the combined use of chemically induced primary
cancer models and molecular imaging techniques may help to develop new anticancer diagnostics and
therapeutics.