CART1 gene, located on q11-q12 region of the chromosome 17 long arm, is commonly amplified in human breast carcinomas. The CART1 protein contains several motifs known as the RING, CART, and TRAF domains. The RING domain is cysteine rich (C3HC3D) and is located at the N-terminus. The CART domain is centrally located in the protein and is a cysteine-rich region composed of three repeats of HC3HC3. The TRAF domain is located at the C-terminus and is involved in protein-protein interactions. These domains are also found in the human CD40-binding protein and the mouse TNF receptor-associated factor 2 (TRAF2), which are involved in TNF receptor signaling pathways. CART1 is also known as TRAF4 and is a member of the TRAF family of proteins. TRAF4/CART1 is expressed in breast carcinomas and metastatic axillary lymph nodes, while the mRNA is found in malignant epithelial cells. Immunohistochemistry of a breast carcinoma revealed that TRAF4 is located within the nucleus. Therefore, TRAF4 may play a role in the development of breast carcinomas via TNF-dependent signaling pathways.