The NUDCD1 gene encodes the 583 amino acid CML66 protein which demonstrates expression in a variety of solid tumor cell lines and leukemias. Expression of CML66 in normal tissues is restricted to testis and heart. The CML66 antibody is found in sera of 18-38% of patients with lung cancer, melanoma or prostate cancer. These findings indicate that CML66 may be immunogenic in a wide variety of malignancies and may be a target for antigen-specific immunotherapy. A short isoform of CML66, designated CML66-S, is a product of alternative splicing. CML66-S has the same C-terminus as full-lenghth CML66 (also designated CML66-L), but has a unique N-terminus. CML66-S shows predominant expression in testis, and is also expressed in very low levels in tumor cells, while CML66 is expressed in tumor cells and testis.