The decreasing trend of cancer mortality has been mostly due to the improved diagnostic techniques for detecting the early stage of cancer as well as development of therapeutic strategy which heavily depends on the understanding of the fundamental biology of tumor cell. We applied a systematic study by using bioinformatics and computational biology methods on gene expression data to address problems that related to those two issues. (1).A comparative study of public gene-expression data of seven types of cancers was conducted with the aim of deriving serum marker genes for early detection, The analysis results indicate that (1a) each cancer type can be distinguished from its corresponding control tissue based on the expression patterns of a small number of genes; (1b) the expression patterns of some genes can distinguish multiple cancer types from their corresponding control tissues, potentially serving as general markers for all or some groups of cancers; (1c) the proteins encoded by some of these genes are predicted to be blood secretory providing potential cancer markers in blood. (2). A comparative analysis of two types of skin cancers, melanoma and basal cell carcinoma in comparison with other cancer types, was conducted with the aim of improving the understanding and identifying key regulatory factors that either cause or contribute to the aggressiveness of melanoma. Our findings include the following. (2a) Advanced melanoma shows substantial up-regulation of key genes involved complimentary metabolism process, providing a source of the energetics necessary to support the rapid growth. (3) A comparative analysis of six solid cancer types in micro-environmental study with the aim of proposing a model of how cancer cells utilize a few mechanisms to keep the protons outside of the cells. (3a)The model consists of a number of previously studied, well or partially, mechanisms for transporting out the excess protons and a new mechanism that neutralizes protons. (3b)We hypothesize that these processes are regulated by cancer related conditions making these encoded processes not available to normal cells under acidic conditions. We believe this systematic study will bring important insight regarding to both topics to the cancer research field.