During the past decade, the role of the ERBB2(neu/HER2) oncogene as an important predictor of patient outcome and response to various therapies in breast cancer has been clearly established. The C35 (C17orf37) is a novel tumor biomarker abundantly expressed in breast cancer. Identification of shared tumor-specific targets is useful in developing broadly applicable therapies. The C35 gene is located on chromosome 17q12, 505nucleotides from the 3' end of the ERBB2oncogene, the antigenic target for trastuzumab(Herceptin) therapy. The chromosomal arrangement of the genes encoding C35 andERBB2 is tail to tail.