Thymopoietin (TMPO) is an inner nuclear membrane protein, the coding gene named equally, can give arise to six isoforms by alternative splicing. This gene has been found up regulated in several types of cancer. At present work, we evaluated the TMPO isoforms generated by alternative splicing as well as the protein signal detection in breast cancer samples. TMPO expression was analyzed by immunohistochemistry in tissue microarray containing 46 breast tissue samples including normal (n = 6), benign lesions (n = 18) (fibroadenomas (n = 6), fibrocystic changes (n = 6), ductal hyperplasias (n = 6)) and breast carcinoma (n = 22). Isoforms -α, -β and -γ of TMPO were evaluated using RT-PCR; clinical-pathological correlation analysis were done by mean of X(2). Neither the normal nor the benign lesions of the breast showed positive TMPO immunodetection, whilst 45 % of the breast carcinomas were immunopositive (p = 0.000), nine of ten positives carcinomas correspond to the Luminal A subtype. Further, alpha isoform was present in all breast samples analyzed; however, beta and gamma isoforms were only present in ten (p = 0.003) and 17 (p = 0.000), respectively, in the breast cancer samples. According with the present data, we suggest that TMPOβ and -γ isoforms could provide a potential reliable diagnostic marker for breast cancer.