Gain of chromosome 1q31-1q32 is seen in >50% of retinoblastoma and is common in other tumors. To define the minimal 1q region of gain, we determined genomic copy number by quantitative multiplex PCR of 14 sequence tagged sites (STSs) spanning 1q25.3-1q41. The most frequently gained STS at 1q32.1 (71%; 39 of 55 retinoblastoma) defined a 3.06 Mbp minimal region of gain between flanking markers, containing 14 genes. Of these, only KIF14, a putative chromokinesin, was overexpressed in various cancers by real-time RT-PCR. KIF14 mRNA was expressed in 20/22 retinoblastoma samples 100-1000-fold higher than in retina (t-test P=0.00002); cell lines (n=10) had higher levels than tumors (n=12) (P=0.009). KIF14 protein was overexpressed in retinoblastoma tumors and breast cancer cell lines by immunoblot. KIF14 was expressed in 4/4 breast cancer cell lines 31-92-fold higher than in normal breast tissue, in 5/5 medulloblastoma cell lines 22-79-fold higher than in fetal brain, and in 10/22 primary lung tumors 3-34-fold higher than in normal lung. Patients with lung tumors that overexpress KIF14 showed a trend toward decreased survival. KIF14 may thus be important in oncogenesis, and has promise as a prognostic indicator and therapeutic target.