Investigation of cancer gene expression profile in context of tissue-specific genes hasn’t been studied in detail. In this study, we aim to understand genetic alteration of tumors in context of tissue-specific genes. Specific genes for various healthy tissues were determined using extended tau which is a robust and rigorous method generated in our previous study. Tissue-specific genes were joined with breast cancer expression data. Utilizing a statistical approach, we identified genes which are specific to a tissue other than breast but having high expression in cancerous breast, not in normal breast. We pinpointed 34 genes specifically expressed in breast cancer, although they are specific to ovary, placenta or testis. This unsuspected phenomenon was also observed in different cancers. Some of cancer-testis genes, MAGE, TEX and PAGE family members, have been confirmed by our study and we observed additional cancer-testis genes such as CT83, SPANX family members. Several placenta and testis- specific genes are highly expressed in only breast cancer, while some of them are also expressed in lung and liver cancer. Consequently, detected genes have potential to be adopted as early diagnostic markers and immunogenic therapeutics. Germline and placental genes should be studied in detail to reveal cancer cells behaviors.