Background Detection of circulating tumor cells (CTC) by techniques based on epithelial
cell adhesion molecule (EpCAM) is suboptimal in urothelial carcinoma (UC). As HER2
is thought to be broadly expressed in UC, we explored its utility for CTC detection.
Methods HER2 and EpCAM expression was analyzed in 18 UC cell lines (UCCs) by qRT-PCR,
western blot and fluorescence-activated cell scanning (FACS) and compared to the strongly
HER2-expressing breast cancer cell line SKBR3 and other controls. HER2 expression
in UC patient tissues was measured by qRT PCR and correlated with data on survival
and risk for metastasis. UCCs with high EpCAM and variable HER2 expression were used
for spike-in experiments in the CellSearch system. Twenty-one blood samples from 13
metastatic UC patients were analyzed for HER2-positive CTCs with CellSearch. Results
HER2 mRNA and protein were broadly expressed in UCC, with some heterogeneity, but
at least 10-fold lower than in the HER-2+ SKBR3 cells. Variations were unrelated to
cellular phenotype or clinicopathological characteristics. EpCAM expression was essentially
restricted to UCCs with epitheloid phenotypes. Heterogeneity of EpCAM and HER2 expression
was observed also in spike-in experiments. The 7 of 21 blood samples from 6 of 13
patients were enumerated as CTC positive via EpCAM, but only one sample stained weakly
positive (1+) for HER2. Conclusions Detection rate of CTCs by EpCAM in UC is poor,
even in metastatic patients. Because of its widespread expression, particularly in
patients with high risk of metastasis, detection of HER2 could improve identification
of UC CTCs, which is why combined detection using antibodies for EpCAM and HER2 may
be beneficial.
