Gain of chromosome 1q is a hallmark of breast cancer, and likely reflects oncogene amplification. We previously identified mitotic kinesin KIF14 (kinesin family member 14) as an overexpressed candidate oncogene in the 1q31.3-1q32.1 minimal region of genomic gain in breast cancer cell lines. KIF14 also showed high expression in other cancers, notably an association with survival in lung tumors. We now report KIF14 expression in 99 primary breast tumors and 10 normal breast controls. Measured by realtime RT-PCR, KIF14 was overexpressed 10-fold on average in tumors relative to normals (t test p 5 0.000054); expression increased with grade (ANOVA p 5 0.000006). Infiltrating ductal carcinomas had higher KIF14 levels than lobular (p 5 0.017), and estrogen receptor (ER) negative tumors had higher KIF14 levels than ER positive tumors (t test p 5 0.030). KIF14 expression correlated positively with Ki-67 mRNA level (Spearman r 5 0.692, p 5 0.000001), fraction of positive nodes (r 5 0.227, p 5 0.024) and percent invasive cells (r 5 0.360, p 5 0.0002), and negatively with percent fatty stroma (r 5 20.258, p 5 0.010) and percent normal epithelium (r 5 20.291, p 5 0.003). KIF14 expression is thus tumor-specific and increased in more aggressive tumors. Indeed, KIF14 expression predicted overall survival (univariate Cox p 5 0.010), with an odds ratio of 3.60 (1.37-9.48), in 50 tumors with available outcome data. KIF14 overexpression also predicted decreased disease-free survival (log-rank p 5 0.049). These findings are the first evidence of association between expression of a mitotic kinesin and prognostic variables in breast cancer. ' 2006 Wiley-Liss, Inc.Key words: breast cancer; KIF14; kinesin; prognosis; real-time RT-PCR Recurrent chromosomal gains and losses are a feature of most cancers, and are presumed to reflect underlying oncogene amplification and tumor suppressor gene loss, respectively. In breast cancer, gain of 1q is the second-most common genomic gain (after 8q). Based on cumulative data in the Progenetix database of cytogenetic changes in cancer, 1 the minimal common region of genomic gain encompasses bands 1q31-1q32, gained or amplified in 44% of the 631 breast tumors in the database. 1 Gain of the long arm of chromosome 1 is one of the most frequent genomic aberrations in many tumor types, including retinoblastoma, strongly suggesting the presence of oncogene(s) in this region.Using quantitative multiplex PCR of genetic markers across the 1q31-1q32 region of chromosomal gain, we previously scanned DNA from 55 retinoblastoma and 12 breast cancer cell lines, and identified a 3.06 Mbp minimal region of gain. 2 Reverse transcription (RT)-PCR expression analyses of all genes in this region showed that only KIF14 (kinesin family member 14), a poorly characterized kinesin, was overexpressed 31-to 92-fold in 4 breast cancer cell lines compared with healthy breast tissue. Robust, cell line-specific protein expression, paralleling the mRNA level, was confirmed by immunoblot. KIF14 mRNA was also highly overexpressed in ...