In this study, the tumor area could be clearly detected by single-photon emission computed tomography (SPECT) imaging at 6 h after intravenous injection of 131I-LyP-1 in tumor-bearing mice with MDA-MB-435 cells, and the ratios of tumor to muscle and tumor to blood were 6.3 and 1.1, respectively. Here, PTPN22 is linked to neoplasm.